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We present new Hubble Space Telescope (HST), Gemini South, and Chandra observations of the radio galaxy 0313-192, which hosts a 350 kpc double source and jets, even though previous data have suggested that it is a spiral galaxy. We measure the bulge scale and the luminosity, radial, and vertical profiles of disk starlight and consider the distributions of H II regions and absorbing dust. In each case the HST data confirm its classification as an edge-on spiral galaxy, the only such system known to produce such an extended radio source of this kind. The Gemini near-IR images and Chandra spectral fit reveal a strongly obscured central active galactic nucleus (AGN), seen through the entire interstellar medium path length of the disk and showing X-ray evidence of additional absorption from warm or dense material close to the central object. We consider several possible mechanisms for producing such a rare combination of AGN and host properties, some combination of which may be at work. These include an unusually luminous bulge (suggesting a black hole of mass ∼8 × 10⁸M_⊙), the orientation of the jets near the pole of the gas-rich disk, and some evidence of a weak gravitational interaction that has warped the disk and could have enhanced fueling of the central engine. We detect an X-ray counterpart of the kiloparsec-scale radio jet emerging to the south; jet/counterjet limits on both radio and X-ray regimes allow them to be symmetric if seen more than 15° from the plane of the sky, still consistent with the jet axes being within ∼30° of the poles of the gas-rich galaxy disk. A linear or disklike emission-line structure is seen around the nucleus, inclined by ∼20° to the stellar disk but nearly perpendicular to the jets; this may represent the aftermath of a galaxy encounter, in which gas is photoionized by a direct view of the nuclear continuum.

We discuss spectroscopy and IR photometry for a complete sample of ∼800 galaxies in close pairs objectively selected from the second Center for Astrophysics redshift survey. We use the Two Micron All Sky Survey to compare near-IR color-color diagrams for our sample with the Nearby Field Galaxy Sample and with a set of IRAS flux-limited pairs from Surace and coworkers. We construct a basic statistical model to explore the physical sources of the substantial differences among these samples. The model explains the spread of near-IR colors and is consistent with a picture in which central star formation is triggered by the galaxy-galaxy interaction before a merger occurs. For 160 galaxies we report new, deep JHK photometry within our spectroscopic aperture, and we use the combined spectroscopic and photometric data to explore the physical conditions in the central bursts. We find a set of objects with H - K ≥ 0.45 and with a large F_FIR/F_H. We interpret the very red H - K colors as evidence for 600-1000 K dust within compact star-forming regions, perhaps similar to super star clusters identified in individual well-studied interacting galaxies. The galaxies in our sample are candidate "hidden" bursts or, possibly, "hidden" active galactic nuclei. Over the entire pair sample, both spectroscopic and photometric data show that the specific star formation rate decreases with the projected separation of the pair. The data suggest that the near-IR color-color diagram is also a function of the projected separation; all of the objects with central near-IR colors indicative of bursts of star formation lie at small projected separation.

Many eclipsing binary star systems show long-term variations in their orbital periods, evident in their O - C (observed minus calculated period) diagrams. With data from the Robotic Optical Transient Search Experiment (ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1 m data, and recent American Association of Variable Star Observers (AAVSO) data, we revisit Borkovits and Hegedüs's best-case candidates for third-body effects in eclipsing binaries: AB And, TV Cas, XX Cep, and AK Her. We also examine the possibility of a third body orbiting Y Cam. Our new data support their suggestion that a third body is present in all systems except AK Her, as is revealed by the sinusoidal variations of the O - C residuals. Our new data suggest that a third body alone cannot explain the variations seen in the O - C residuals of AK Her. We also provide a table of 143 eclipsing binary systems that have historical AAVSO O - C data with new values computed from the SkyDOT database.

We are performing a uniform and unbiased imaging survey of the Large Magellanic Cloud (LMC; ∼7° × 7°) using the IRAC (3.6, 4.5, 5.8, and 8 μm) and MIPS (24, 70, and 160 μm) instruments on board the Spitzer Space Telescope in the Surveying the Agents of a Galaxy's Evolution (SAGE) survey, these agents being the interstellar medium (ISM) and stars in the LMC. This paper provides an overview of the SAGE Legacy project, including observing strategy, data processing, and initial results. Three key science goals determined the coverage and depth of the survey. The detection of diffuse ISM with column densities >1.2 × 10²¹ H cm^-2 permits detailed studies of dust processes in the ISM. SAGE's point-source sensitivity enables a complete census of newly formed stars with masses >3 M_⊙ that will determine the current star formation rate in the LMC. SAGE's detection of evolved stars with mass-loss rates >1 × 10^-8M_⊙ yr^-1 will quantify the rate at which evolved stars inject mass into the ISM of the LMC. The observing strategy includes two epochs in 2005, separated by 3 months, that both mitigate instrumental artifacts and constrain source variability. The SAGE data are nonproprietary. The data processing includes IRAC and MIPS pipelines and a database for mining the point-source catalogs, which will be released to the community in support of Spitzer proposal cycles 4 and 5. We present initial results on the epoch 1 data for a region near N79 and N83. The MIPS 70 and 160 μm images of the diffuse dust emission of the N79/N83 region reveal a similar distribution to the gas emissions, especially the H I 21 cm emission. The measured point-source sensitivity for the epoch 1 data is consistent with expectations for the survey. The point-source counts are highest for the IRAC 3.6 μm band and decrease dramatically toward longer wavelengths, consistent with the fact that stars dominate the point-source catalogs and the dusty objects detected at the longer wavelengths are rare in comparison. The SAGE epoch 1 point-source catalog has ∼4 × 10⁶ sources, and more are anticipated when the epoch 1 and 2 data are combined. Using Milky Way (MW) templates as a guide, we adopt a simplified point-source classification to identify three candidate groups—stars without dust, dusty evolved stars, and young stellar objects—that offer a starting point for this work. We outline a strategy for identifying foreground MW stars, which may comprise as much as 18% of the source list, and background galaxies, which may comprise ∼12% of the source list.

We report the detection of ongoing star formation in the prominent tidal arms near NGC 3077 (member of the M81 triplet). In total, 36 faint compact H II regions are identified, covering an area of ∼4 × 6 kpc². Most of the H II regions are found at H I column densities above 1 × 10²¹ cm^-2 (on scales of 200 pc), well within the range of threshold columns measured in normal galaxies. The H II luminosity function resembles those derived for other low-mass dwarf galaxies in the same group; we derive a total star formation rate of 2.3 × 10^-3M_⊙ yr^-1 in the tidal feature. We also present new high-resolution imaging of the molecular gas distribution in the tidal arm using CO observations obtained with the Owens Valley Radio Observatory interferometer. We recover about one-sixth of the CO flux (or M ∼ 2 × 10⁶M_⊙, assuming a Galactic conversion factor) originally detected in the IRAM 30 m single-dish observations, indicating the presence of a diffuse molecular gas component in the tidal arm. The brightest CO peak in the interferometer map (comprising half of the detected CO flux) is coincident with one of the brightest H II regions in the feature. Assuming a constant star formation rate since the creation of the tidal feature (presumably ∼3 × 10⁸ yr ago), a total mass of ∼7 × 10⁵M_⊙ has been transformed from gas into stars. Over this period the star formation in the tidal arm has resulted in an additional enrichment of ΔZ > 0.002. The reservoir of atomic and molecular gas in the tidal arm is ∼3 × 10⁸M_⊙, allowing star formation to continue at its present rate for a Hubble time. Such widespread, low-level star formation would be difficult to image around more distant galaxies but may be detectable through intervening absorption in quasar spectra.

We have analyzed Hubble Space Telescope NICMOS2 F110W-, F160W-, F165M-, and F207M-band images covering the central 1' × 1' region of the cluster associated with Mon R2 in order to constrain the initial mass function (IMF) down to 20M_J. The flux ratio between the F165M and F160W bands was used to measure the strength of the water-band absorption feature and select a sample of 12 out of the total sample of 181 objects that have effective temperatures between 2700 and 3300 K. These objects are placed in the H-R diagram together with sources observed by Carpenter et al. to estimate an age of ∼1 Myr for the low-mass cluster population. By constructing extinction-limited samples, we are able to constrain the IMF and the fraction of stars with a circumstellar disk in a sample that is 90% complete for both high- and low-mass objects. For stars with estimated masses between 0.1 and 1.0 M_⊙ for a 1 Myr population with A_V ≤ 19 mag, we find that 27% ± 9% have a near-infrared excess indicative of a circumstellar disk. The derived fraction is similar to or slightly lower than the fraction found in other star-forming regions of comparable age. We constrain the number of stars in the mass interval 0.08-1.0 M_⊙ to the number of objects in the mass interval 0.02-0.08 M_⊙ by forming the ratio R** = N(0.08-1 M_⊙)/N(0.02-0.08 M_⊙) for objects in an extinction-limited sample complete for A_V ≤ 7 mag. The ratio is found to be R** = 2.2 ± 1.3, assuming an age of 1 Myr, consistent with the similar ratio predicted by the system IMF proposed by Chabrier. The ratio is similar to the ratios observed toward the Orion Nebula Cluster and IC 348, as well as the ratio derived in the 28 deg² survey of Taurus by Guieu et al.

In an attempt to discover short-period, Jupiter-mass planets orbiting solar-type stars in open clusters, we searched for planetary transits in the populous and relatively unstudied open cluster NGC 7086. A color-magnitude diagram constructed from new B and V photometry is presented, along with revised estimates of the cluster's color excess, distance modulus, and age. Several turnoff stars were observed spectroscopically in order to determine a color excess of E(B - V) = 0.83 ± 0.02. Empirically fitting the main sequences of two young open clusters and the semiempirical zero-age main sequence of Vandenberg and Poll yielded a distance modulus of (V - M_V) = 13.4 ± 0.3 mag. This corresponds to a true distance modulus of (m - M)₀ = 10.8 mag or a distance of 1.5 kpc to NGC 7086. These values were used with isochrones from the Padova group to obtain a cluster age of 100 Myr. Eleven nights of R-band photometry were used to search for planetary transits. Differential magnitudes were constructed for each star in the cluster. Light curves for each star were produced on a night-to-night basis and inspected for variability. No planetary transits were apparent; however, some interesting variable stars were discovered: a pulsating variable that appears to be a member of the γ Dor class and four possible eclipsing binary stars, one of which actually may be a multiple system.

We present adaptive optics observations of HD 43587, one of the primary targets of the COROT (Convection, Rotation, and Planetary Transits) asteroseismology and planet-finding space mission and a star that was previously detected as a spectroscopic binary by Vogt and coworkers. We resolve a close companion, which is responsible for the radial velocity variations of the primary. Our observations over a 3 year interval measure the orbital displacement of the companion. Combining these measurements with the radial velocity data of Vogt and coworkers, we solve for the three-dimensional orbit of the system and derive individual masses for HD 43587 and its companion. This is particularly interesting in the perspective of the upcoming COROT mission. These observations were part of a preparatory program for COROT, in which we observed all COROT potential primary targets and some of its secondary targets with adaptive optics. The majority of these stars have potential companions in a 30'' field. Most of these are probably background objects, but some are found within a few arcseconds of the COROT targets and are likely to be true physical companions.

We report on measurements of the ⁴He abundance toward the outer Galaxy H II region S206 with the NRAO Green Bank Telescope. Observations of hydrogen and helium radio recombination lines between 8 and 10 GHz were made toward the peak radio continuum position in S206. We derive ⁴He/H = 0.08459 ± 0.00088 (random) ± 0.0010 (known systematic), 20% lower than optical recombination line results. It is difficult to reconcile the large discrepancy between the optical and radio values even when accounting for temperature, density, and ionization structure or for optical extinction by dust. Using only M17 and S206 we determine ΔY/ΔZ = 1.41 ± 0.62 in the Galaxy, consistent with standard chemical evolution models. High helium abundances in the old stellar population of elliptical galaxies can help explain the increase in UV emission with shorter wavelength between 2000 and 1200 Å, called the "UV upturn" or UVX. Our lower values of ΔY/ΔZ are consistent with a normal helium abundance at higher metallicity and suggest that other factors, such as a variable red giant branch mass loss with metallicity, may be important. When combined with ⁴He abundances in metal-poor galaxy H II regions, Magellanic Cloud H II regions, and M17 that have been determined from optical recombination lines, including the effects of temperature fluctuations, our radio ⁴He/H abundance ratio for S206 is consistent with a helium evolution of ΔY/ΔZ = 1.6. A linear extrapolation to zero metallicity predicts a ⁴He/H primordial abundance ratio about 5% lower than that given by the Wilkinson Microwave Anisotropy Probe and standard big bang nucleosynthesis. The measured ⁴He abundances may be systematically underestimated by a few percent if clumping exists in these H II regions.

We have analyzed archival Hubble Space Telescope Advanced Camera for Surveys images in g and z of the globular cluster (GC) systems of 53 ellipticals in the Virgo Cluster, spanning massive galaxies to dwarf ellipticals (dEs). Several new results emerged. (1) In the giant ellipticals (gEs) M87 and NGC 4649, there is a correlation between luminosity and color for individual blue (metal-poor) GCs, such that more massive GCs are more red (metal-rich). A plausible interpretation of this result is self-enrichment, and a speculative suggestion is that these GCs once possessed dark matter halos. (2) The dispersion in color is nearly twice as large for the metal-rich GCs as for the metal-poor GCs. However, there is evidence for a nonlinear relation between g - z and metallicity, and the dispersion in metallicity may be the same for both subpopulations. (3) Very luminous, intermediate-color GCs are common in gEs. These objects may be remnants of many stripped dwarfs, analogs of ω Cen in the Galaxy. (4) There is a continuity of GC system colors from gEs to some dEs; in particular, many dEs have metal-rich GC subpopulations. We also confirm the GC color-galaxy luminosity relations found previously for both metal-poor and metal-rich GC subpopulations. (5) There are large differences in GC specific frequency among dEs, independent of the presence of a nucleus and the fraction of metal-rich GCs. Over -15 < M_B < -18 we find little correlation between specific frequency and M_B. But we do find evidence for two separate S_N classes of dEs: those with B-band S_N ∼ 2 and those with populous GC systems that have S_N ranging from ∼5 to 20 with median S_N ∼ 10. Together, these points suggest multiple formation channels for dEs in the Virgo Cluster. (6) The peak of the GC luminosity function (GCLF) is the same for both gEs and dEs. This is contrary to expectations of dynamical friction on massive GCs, unless the primordial GCLF varies between gEs and dEs. Among gEs the GCLF turnover varies by a surprisingly small 0.05 mag, an encouraging result for its use as an accurate standard candle.

We present chemical abundances of several proton-capture, α-, Fe-peak, and neutron-capture elements and radial velocities for 21 red giant branch (RGB) and asymptotic giant branch members of the Galactic globular cluster M12. Abundances are based on equivalent width measurements and synthetic spectral analyses of moderate-resolution spectra (R ∼ 15,000) obtained with the 3.5 m WIYN telescope and Hydra multifiber spectrograph. The stars observed range from the RGB tip (M = -2.47) down to about 0.50 mag above the level of the horizontal branch (M = +0.11). Our spectroscopic analysis suggests that M12 is a moderately metal-poor cluster with [Fe/H] = -1.54 (σ = 0.09). While the Na abundances exhibit a range of 0.90 dex, Mg and Al abundances are enhanced by 0.37 and 0.54 dex and are nearly constant at all RGB luminosities, in contrast to the blue horizontal-branch cluster M13. The α- and Fe-peak elements indicate that M12 has undergone a similar chemical enrichment history to that of globular clusters and field stars of comparable metallicity, with ⟨[α/Fe]⟩ = +0.33 (σ = 0.11). M12 also appears to be slightly r-process-rich, with ⟨[Eu/Ba,La]⟩ = +0.22 (σ = 0.18).

Astrometric measurements for 25 red dwarf systems are presented, including the first definitive trigonometric parallaxes for 20 systems within 10 pc of the Sun, the horizon of the RECONS sample. The three nearest systems that had no previous trigonometric parallaxes (other than perhaps rough preliminary efforts) are SO 0253+1652 (3.84 ± 0.04 pc, the 23rd nearest system), SCR 1845-6357 AB (3.85 ± 0.02 pc, 24th nearest), and LHS 1723 (5.32 ± 0.04 pc, 56th nearest). In total, seven of the systems reported here rank among the nearest 100 stellar systems. Supporting photometric and spectroscopic observations have been made to provide full characterization of the systems, including complete VRIJHK_s photometry and spectral types. A study of the variability of 27 targets reveals six obvious variable stars, including GJ 1207, for which we observed a flare event in the V band that caused it to brighten by 1.7 mag. Improved parallaxes for GJ 54 AB and GJ 1061, both important members of the 10 pc sample, are also reported. Definitive parallaxes for GJ 1001 A, GJ 633, and GJ 2130 ABC, all of which have been reported to be within 10 pc, indicate that they are beyond 10 pc. From the analysis of systems with (previously) high trigonometric parallax errors, we conclude that parallaxes with errors in excess of 10 mas are insufficiently reliable for inclusion in the RECONS sample. The cumulative total of new additions to the 10 pc sample since 2000 is now 34 systems: 28 by the RECONS team and six by other groups. This total represents a net increase of 16% in the number of stellar systems reliably known to be nearer than 10 pc.

We present the first far-red spectra of the L subdwarf 2MASS J16262034+3925190 and the late-M/early-L subdwarf 2MASS J16403197+1231068. We confirm the ultracool subdwarf nature of these objects. Like an L4 dwarf, 2M 1626+3925 shows strong K I absorption and is very similar to, but hotter than, the late-L subdwarf 2MASS J05325346+8246465. It is unambiguously an L subdwarf. 2M 1640+1231 is very similar to SSSPM J1444-2019, which has been classified as sdM9 or early sdL. In contrast to the hotter M subdwarfs, L subdwarfs are characterized by not only enhanced hydrides but also strong TiO. Progress in a classification system requires identification of more subdwarfs to map out their variations.

Errors in the kinematic distances, under the assumption of circular gas orbits, were estimated by performing synthetic observations of a model disk galaxy. It was found that the error is <0.5 kpc for most of the disk when the measured rotation curve is used, but larger if the real rotation curve is applied. In both cases, the error is significantly larger at the positions of the spiral arms. The error structure is such that, when kinematic distances are used to develop a picture of the large-scale density distribution, the most significant features of the numerical model are significantly distorted or absent, while spurious structure appears. By considering the full velocity field in the calculation of the kinematic distances, most of the original density structures can be recovered.

We report subarcsecond-resolution Very Large Array imaging of four nearby spiral galaxies: IC 342, Maffei II, NGC 2903, and NGC 6946. In each galaxy, compact radio continuum sources are identified in the central ∼15'' × 15'' region. These compact sources are responsible for 20%-30% of the total emission from the central kiloparsec of the host galaxies at 2 cm but only ∼5%-10% at 6 cm. More than half of the compact sources appear to be H II regions. The H II regions with rising spectra must be fairly dense (n_i ∼ 10⁴ cm^-3) and are presumably very young. The largest of these H II regions require the excitation of 500-800 O stars within regions only a few parsecs in extent. These clusters approach the sizes expected for globular clusters. Thermal free-free emission from compact sources contributes more significantly at 2 cm, while diffuse synchrotron emission dominates at 6 cm. The radio H II regions are found near the centers of giant molecular clouds in projection and do not have obvious visual counterparts.

New millimeter-wave CO and HCN observations of the host galaxies of infrared-excess Palomar-Green (PG) quasi-stellar objects (QSOs) previously detected in CO are presented. These observations are designed to assess the validity of using the infrared luminosity to estimate star formation rates of luminous active galactic nuclei (AGNs) by determining the relative significance of dust heating by young, massive stars and AGNs in QSO hosts and IRAS galaxies with warm, AGN-like infrared colors. The analysis of these data is based, in part, on evidence that HCN traces high-density (>10⁴ cm^-3) molecular gas, and that the starburst-to-HCN luminosity ratio, L_SB/L, of IRAS-detected galaxies is constant. The new CO data provide a confirmation of prior claims that PG QSO hosts have high infrared-to-CO luminosity ratios, L_IR/L, relative to IRAS galaxies of comparable L_IR. Such high L_IR/L ratios may be due to significant heating of dust by the QSO or to an increased star formation efficiency in QSO hosts relative to the bulk of the luminous IRAS galaxy population. The HCN data show a similar trend, with the PG QSO host I Zw 1 and most of the warm IRAS galaxies having high L_IR/L (>1600) relative to the cool IRAS galaxy population, for which the median ⟨L_IR/L⟩_cool ∼ 890. If the assumption is made that the infrared emission from cool IRAS galaxies is reprocessed light from embedded star-forming regions, then high values of L_IR/L are likely the result of dust heating by the AGNs. Further, if the median ratio of L/L ∼ 0.06 observed for Seyfert galaxies and I Zw 1 is applied to the PG QSOs not detected in HCN, then the derived L_IR/L values correspond to a stellar contribution to the production of L_IR of ∼7%-39%, and star formation rates of ∼2-37 M_⊙ yr^-1 are derived for the QSO hosts. The corresponding values for the warm galaxies are ∼10%-100% and ∼3-220 M_⊙ yr^-1. Alternatively, if the far-infrared is adopted as the star formation component of the total infrared in cool galaxies, i.e., ⟨L_FIR/L⟩_cool ∼ L_SB/L, the stellar contributions in QSO hosts and warm galaxies to their L_FIR are up to 35% and 10% higher, respectively, than the percentages derived for L_IR. This raises the possibility that the L_FIR in several of the PG QSO hosts, including I Zw 1, could be due entirely to dust heated by young, massive stars. Finally, there is no evidence that the global HCN emission is enhanced relative to CO in galaxies hosting luminous AGNs.

We present the first results from the Australia Telescope Large Area Survey, which consists of deep radio observations of a 3.7 deg² field surrounding the Chandra Deep Field-South, largely coincident with the infrared Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey. We also list cross-identifications to infrared and optical photometry data from SWIRE, and ground-based optical spectroscopy. A total of 784 radio components are identified, corresponding to 726 distinct radio sources, nearly all of which are identified with SWIRE sources. Of the radio sources with measured redshifts, most lie in the redshift range 0.5-2 and include both star-forming galaxies and active galactic nuclei. We identify a rare population of infrared-faint radio sources that are bright at radio wavelengths but are not seen in the available optical, infrared, or X-ray data. Such rare classes of sources can only be discovered in wide, deep surveys such as this.

NGC 5128, a giant elliptical galaxy only ∼4 Mpc away, is the dominant member of a galaxy group of over 80 probable members. The Centaurus group provides an excellent sample for a kinematic comparison between the halo of NGC 5128 and its surrounding satellite galaxies. A new study, presented here, shows no kinematic difference in rotation amplitude, rotation axis, or velocity dispersion between the halo of NGC 5128, determined from over ∼340 of its globular clusters, and those of the Centaurus group as a whole. These results suggest NGC 5128 could be behaving in part as the inner component to the galaxy group, and could have begun as a large initial seed galaxy, gradually built up by minor mergers and satellite accretions, consistent with simple cold dark matter models. The masses and mass-to-light ratios in the B band, corrected for projection effects, are determined to be (1.3 ± 0.5) × 10¹²M_⊙ and 52 ± 22 M_⊙L for NGC 5128 out to a galactocentric radius of 45 kpc and (9.2 ± 3.0) × 10¹²M_⊙ and 153 ± 50 M_⊙L for the Centaurus group, consistent with previous studies.

Despite the common picture of an early-type dwarf galaxy (dE) as a quiescent galaxy with no star formation and little gas, we identify 23 dEs that have blue central colors caused by recent or ongoing star formation in our sample of 476 Virgo Cluster dEs. In addition, 14 objects that were mostly classified as (candidate) blue compact dwarfs have similar properties. Among the certain cluster members, the dEs with blue centers reach a fraction of more than 15% of the dE population at brighter (m_B ≤ 16) magnitudes. A spectral analysis of the centers of 16 galaxies reveals in all cases an underlying old population that dominates the mass, with M_old ≥ 90% for all but one object. Therefore, the majority of these galaxies will appear like ordinary dEs within approximately one gigayear or less after the last episode of star formation. Their overall gas content is less than that of dwarf irregular galaxies but higher than that of ordinary dEs. Their flattening distribution suggests the shape of a thick disk, similar to what has been found for dEs with disk features in Paper I of this series. Their projected spatial distribution shows no central clustering, and their distribution with projected local density follows that of irregular galaxies, indicative of an unrelaxed population. This is corroborated by their velocity distribution, which displays two side peaks characteristic of recent infall. We discuss possible formation mechanisms (ram-pressure stripping, tidally induced star formation, and harassment) that might be able to explain both the disk shape and the central star formation of the dEs with blue centers.

From histories of reddening studies for the Hyades, Praesepe, and nearby field stars, it is concluded that reddening scholarship requires fundamental reform. The adopted protocol for the reformed version of scholarship includes (1) rigorous published foundations for reddening values, (2) explicit quality control of reddening techniques, (3) use of techniques with limited metallicity sensitivity, (4) explicit zero-point control for both input data and derived reddening values, (5) an explicit choice of a reddening zero point, and (6) adherence to statistical norms. It is argued that only limited use should be made of reddening values from (1) spectral types for F0 and later type stars, (2) UBV analysis of blanketed stars, and (3) certain published relations between reddening and distance. However, reddening values may be based safely on (1) polarization measurements, (2) comparisons of β and (R - I)_C for F stars, and (3) Strömgren β analysis of A stars. For the Hyades and Coma, upper 95% confidence limits on E(B - V) are found to be ≤1.0 and ≤3.2 mmag, respectively. For Praesepe, the derived value of E(B - V) is 27 ± 4 mmag. The latter result is obtained after an allowance is made for the effects of an anomalous relation between b - y and (R - I)_C in Praesepe A stars. A test of the possibility that differential stellar rotation causes the anomaly yields an inconclusive result. Adoption of the revised reddening value instead of the canonical value of zero yields an increase in the derived Praesepe distance modulus by 0.14 mag and a decrease in the derived cluster age by about 11%. In addition, by using published high-dispersion results, it is found that the value of [Fe/H] for Praesepe that is consistent with the derived reddening value is +0.01 ± 0.04 dex. Further results for Praesepe stars will be required for a definitive comparison of the Hyades and Praesepe metallicities.

We present mid-IR N-band (λ_eff = 10.2 μm) photometry of a carefully selected sample of T Tauri stars thought to be single from the Taurus-Auriga molecular cloud. Infrared excesses in these stars are generally attributed to circumstellar dust disks. Combining observations at 2.16 (K_s band) and 10.2 μm (N band) we probe a region in the circumstellar dust disk from a few stellar radii through the terrestrial planet zone (0.02-1.0 AU). By analyzing the distribution of the (K_s - N) color index with respect to previously measured photometric rotation periods we investigate what role circumstellar disks play in the rotational evolution of the central star. The resulting positive correlation between these two variables is consistent with the notion that a star-disk interaction facilitates the regulation of angular momentum during the T Tauri stage. We also demonstrate how including nonsingle stars in such an analysis weakens any correlation in the relation between (K_s - N) color and period. To further understand disk properties we also present spectral energy distributions for a few objects with new ground-based M-band (λ_eff = 4.8 μm) and Q-band (λ_eff = 20 μm) data and compare them to a geometrically thin, optically thick disk model.

An analysis of 15 speckle observations taken at the Lowell-Tololo Telescope at Cerro Tololo Inter-American Observatory and 6 speckle observations taken at the WIYN Telescope at Kitt Peak National Observatory indicates that it is possible to characterize the separations, position angles, and magnitude differences of binary stars down to at least one quarter of the diffraction limit with CCD-based speckle imaging. This is made possible by the fact that CCD-based speckle imaging permits the retrieval of reliable photometric information from speckle data, and therefore the elongation of the speckles due to a blended companion may be reliably measured. When observations in two colors are obtained, atmospheric dispersion, which also affects the speckle shape, can be distinguished from binarity in a large number of cases. A regimen for observing sub-diffraction-limited speckle binaries is proposed that could lead to efficient surveys of small-separation binary stars.

Our differential BV photometric observations, acquired with an automated telescope at Fairborn Observatory, show that HD 71636 is an eclipsing binary. From follow-up red-wavelength spectroscopic observations we classify the primary and secondary as an F2 dwarf and an F5 dwarf, respectively. The system has a period of 5.01329 days and a circular orbit. We used the Wilson-Devinney program to simultaneously solve our BV light curves and radial velocities and determined a number of fundamental properties of the system. Comparison with evolutionary tracks indicates that both stars are well ensconced on the main sequence. The age of the system is about 1.2 billion years.

We present optical and near-infrared images, H I 21 cm emission maps, optical spectroscopy, and Hubble Space Telescope Space Telescope Imaging Spectrograph ultraviolet spectroscopy of the QSO/galaxy pair SBS 1122+594/IC 691. The QSO sight line lies at a position angle of 27° from the minor axis of the nearby dwarf starburst galaxy IC 691 (cz_gal = 1204 ± 3 km s^-1, L_B ∼ 0.09L*, current star formation rate = 0.08-0.24 hM_⊙ yr^-1) and 33 h kpc (66) from its nucleus. We find that IC 691 has an H I mass of M = (3.6 ± 0.1) × 10⁸M_⊙ and a dynamical mass of M_dyn = (3.1 ± 0.5) × 10¹⁰hM_⊙. The UV spectrum of SBS 1122+594 shows a metal-line (Lyα+C IV) absorber near the redshift of IC 691 at cz_abs = 1110 ± 30 km s^-1. Since IC 691 is a dwarf starburst and the SBS 1122+594 sight line lies in the expected location for an outflowing wind, we propose that the best model for producing this metal-line absorber is a starburst wind from IC 691. We place consistent metallicity limits on IC 691 ([Z/Z_⊙] ∼ -0.7) and the metal-line absorber ([Z/Z_⊙] < -0.3). We also find that the galaxy's escape velocity at the absorber location is v_esc = 80 ± 10 km s^-1 and derive a wind velocity of v_w = 160 ± 50 km s^-1. Thus, the evidence suggests that IC 691 produces an unbound starburst wind that escapes from its gravitational potential to transport metals and energy to the surrounding intergalactic medium.

We present a spectroscopic study and dynamical analysis of ∼2600 M7 dwarfs. We confirm our previous finding that the fraction of magnetically active stars decreases with vertical distance from the Galactic plane. We also show that the mean luminosity of the Hα emission has a small but statistically significant decrease with distance. Using space motions for ∼1300 stars and a simple one-dimensional dynamical simulation, we demonstrate that the drop in the activity fraction of M7 dwarfs can be explained by thin disk dynamical heating and a rapid decrease of magnetic activity at a mean stellar age of ∼6-7 Gyr.

A planet is an end product of disk accretion around a primary star or substar. I quantify this definition by the degree to which a body dominates the other masses that share its orbital zone. Theoretical and observational measures of dynamical dominance reveal gaps of 4-5 orders of magnitude separating the eight planets of our solar system from the populations of asteroids and comets. The proposed definition dispenses with upper and lower mass limits for a planet. It reflects the tendency of disk evolution in a mature system to produce a small number of relatively large bodies (planets) in nonintersecting or resonant orbits, which prevents collisions between them.

We present values for the masses of Saturn and its major satellites, the zonal harmonics in the spherical harmonic expansion of Saturn's gravitational potential, and the orientation of the pole of Saturn. We determined these values using an extensive data set: satellite astrometry from Earth-based observatories and the Hubble Space Telescope; Earth-based, Voyager 1, and Voyager 2 ring occultation measurements; Doppler tracking data from Pioneer 11; and Doppler tracking, radiometric range, and imaging data from Voyager 1, Voyager 2, and Cassini.

In order to complete our H I survey of galaxies in the Sculptor group area, Very Large Array observations of NGC 24 and NGC 45 are presented. These two galaxies of similar magnitude, M_B ∼ -17.4, lie in the background of the Sculptor group and are low surface brightness galaxies, especially NGC 45. The H I distribution and kinematics are regular for NGC 24, while NGC 45 exhibits a kinematical twist of its major axis. A tilted-ring model shows that the position angle of the major axis changes by ∼25°. A best-fit model of their mass distributions gives mass-to-light ratios for the stellar disk of 2.5 and 5.2 for NGC 24 and NGC 45, respectively. These values are higher than those expected from stellar population synthesis models. Despite the large dark matter contribution, the galaxy mass is still dominated by the stellar component in their very inner regions. These high mass-to-light ratios are typical of what is seen in low surface brightness galaxies and may indicate that, in those galaxies, disks are far from the maximum disk case. The halo parameters derived from the best-fit models are thus lower limits.

We find nine nuclear cluster candidates in a sample of 14 edge-on, late-type galaxies observed with the Hubble Space Telescope Advanced Camera for Surveys. These clusters have magnitudes (M_I ∼ -11) and sizes (r_eff ∼ 3 pc) similar to those found in previous studies of face-on, late-type spirals and dE galaxies. However, three of the nuclear clusters are significantly flattened and show evidence for multiple, coincident structural components. The elongations of these three clusters are aligned to within ∼10° of the galaxies' major axes. Structurally, the flattened clusters are well fit by a combination of a spheroid and a disk or ring, with the disk preferred in two of three cases. The nuclear cluster disks/rings have F606W - F814W (∼V - I) colors 0.3-0.6 mag bluer than the spheroid components, suggesting that the stars in these components have ages <1 Gyr. In NGC 4244, the nearest of the nuclear clusters, we further constrain the stellar populations via spectroscopy and multiband photometry. This nuclear cluster is equally well fit by single stellar populations with ages of either ∼70 Myr or ∼0.8 Gyr and with masses of ∼3 × 10⁶M_⊙. However, significantly better fits to the spectroscopy and photometry are obtained by combining two or more stellar populations. Exploiting emission lines that appear to originate ∼1'' from the NGC 4244 nucleus, we determine a lower limit on the dynamical mass of 2.5 × 10⁶M_⊙ within 19 pc, typical of values found for other nuclear clusters. We also present tentative evidence that another of the nuclear clusters (in NGC 4206) may also host a supermassive black hole. Based on our observational results we propose an in situ formation mechanism for nuclear clusters in which stars form episodically in compact nuclear disks and then lose angular momentum or heat vertically to form an older spheroidal structure. We estimate the period between star formation episodes to be ∼0.5 Gyr and discuss possible mechanisms for transforming the disklike components into spheroids. We also note the connection between our objects and massive globular clusters (e.g., ω Cen), ultracompact dwarfs, and supermassive black holes.

We have detected, for the first time, Cepheid variables in the Sculptor Group SB(s)m galaxy NGC 55. From wide-field images obtained in the optical V and I bands during 77 nights in 2002-2003, we have found 143 Cepheids with periods ranging from 5.6 to 175.9 days; 133 of these objects have periods longer than 10 days, making NGC 55 to date the galaxy with the largest known number of long-period Cepheids in the Sculptor Group. We construct period-luminosity relations from our data and obtain distance moduli corrected for the small foreground reddening to NGC 55 of 26.79 ± 0.04 mag (internal error) in V, 26.66 ± 0.03 mag in I, and 26.40 ± 0.05 mag in the reddening-independent V - I Wesenheit index. The trend of increasing distance moduli with shorter wavelength hints at the existence of significant reddening intrinsic to NGC 55, which affects the measured Cepheid magnitudes. From our data we determine the intrinsic mean reddening of the Cepheids in NGC 55 as E(B - V) = 0.102 mag, which brings the distance determinations from the different bands into excellent agreement. Our best distance estimate for NGC 55 from the present optical Cepheid photometry is 26.40 ± 0.05 (internal error) ±0.09 mag (systematic error). This value is tied to an assumed LMC distance of 18.50 mag. Our quoted systematic error of the present NGC 55 Cepheid distance does not take into account the current uncertainty in the distance of the fiducial LMC galaxy itself. Within the small respective uncertainties, the Sculptor Group galaxies NGC 55 and NGC 300 are at the same distance of 1.9 Mpc, strengthening the case for a physical association of these galaxies.

We present new results of a spectroscopic survey of circumstellar H I in the direction of evolved stars made with the Nançay Radiotelescope. The H I line at 21 cm has been detected in the circumstellar shells of a variety of evolved stars: asymptotic giant branch stars, oxygen-rich and carbon-rich stars, semiregular and Mira variables, and planetary nebulae. The emissions are generally spatially resolved, i.e., larger than 4', indicating shell sizes on the order of 1 pc, which opens the possibility of tracing the history of mass loss over the past ∼10⁴-10⁵ yr. The line profiles are sometimes composite. The individual components generally have a quasi-Gaussian shape; in particular, they seldom show the double-horn profile that would be expected from the spatially resolved optically thin emission of a uniformly expanding shell. This probably implies that the expansion velocity decreases outward in the external shells (0.1-1 pc) of these evolved stars. The H I line profiles do not necessarily match those of the CO rotational lines. Furthermore, the centroid velocities do not always agree with those measured in the CO lines and/or the stellar radial velocities. The H I emissions may also be shifted in position with respect to the central stars. Without excluding the possibility of asymmetric mass ejection, we suggest that these two effects could also be related to a nonisotropic interaction with the local interstellar medium. H I was detected in emission toward several sources (ρ Per, α Her, δ² Lyr, U CMi) that otherwise have not been detected in any radio lines. Conversely, it was not detected in the two oxygen-rich stars with substantial mass-loss rate, NML Tau and WX Psc, possibly because these sources are young, with hydrogen in molecular form, and/or because the temperature of the circumstellar H I gas is very low (<5 K).

We present Very Large Array observations at 1.3 cm of several water maser detections obtained by previous single-dish studies of Bok globules in the 1988 Clemens and Barvainis (CB) catalog. We report water maser emission in CB 3 (CB 3-mm), CB 54 (IRAS 07020-1618), CB 101 (IRAS 17503-0833), and CB 232 (IRAS 21352+4307) and nondetection toward CB 65 (IRAS 16277-2332) and CB 205 (IRAS 19433+2743). These are the first reported interferometric observations of water masers in Bok globules of the CB catalog. We also present single-dish observations of millimeter and centimeter spectral lines toward CB 101 (IRAS 17503-0833) and CB 65 (IRAS 16277-2332). All the maser emission seems to be associated with star-forming regions hosting bipolar molecular outflows, except IRAS 17503-0833 in CB 101, which we suggest to be a possible Mira evolved star, and IRAS 16277-2332 in CB 65, which is of unknown nature. We have used the precise position of the maser emission to derive information about the powering source of the masers. By analyzing the spatio-kinematical distribution of the water masers, we confirm the millimeter source CB 3-mm as the most likely powering source of the CB 3 masers. We propose the near-IR source CB 232 YC1-I as the best candidate for pumping the maser emission observed in CB 232, while in CB 54 we suggest that the pumping source of the masers could be located at the position of an elongated feature observed in near-IR maps.

We investigate the types of nuclear environments that produce OH megamasers (OHMs) with a study of the optical spectra of 40 OHM host galaxies and a control sample of 30 nonmasing (ultra)luminous infrared galaxies ([U]LIRGs). The optical spectrophotometry provides spatially resolved spectra of multiple nuclei in a few of these merging systems. Of the 40 OHMs classified, 33% are starbursts, 42% are LINERs, and 25% are Seyfert 2 galaxies; the classification of the nonmasing control sample is similar. The OHM fraction in mergers does not depend on nuclear classification, and there are no distinguishing spectral properties to differentiate OHMs from nonmasing mergers; OHM galaxies appear to represent the same optical population as the (U)LIRGs. There are likewise few trends between OHM host-galaxy properties and the properties of the OHMs they produce. OHMs do appear to be somewhat blueshifted with respect to their hosts, particularly LINERs, and Seyfert and LINER hosts tend to produce broader OH emission-line profiles than pure starburst hosts. This suggests that OHMs are in some cases associated with outflows and that the phase space available for masing in LINER and Seyfert hosts is larger than in pure starbursts. The paucity of significant correlations between OHMs and the optical properties of their hosts is presumably due to the severe dust extinction found in (U)LIRGs, especially at the high-density sites of molecular masing.

We present recent measurements of the orbital motion in the binaries DF Tau and ZZ Tau and in the triples Elias 12, T Tau, and V853 Oph. We observed these systems with the Fine Guidance Sensors on the Hubble Space Telescope and with adaptive optics imaging at the W. M. Keck and Gemini North Observatories. Based on our measurements and those presented in the literature we perform preliminary orbital analyses for DF Tau, ZZ Tau, Elias 12 Na-Nb, and T Tau Sa-Sb. Because the orbital coverage in most of these systems does not yet span a sufficient portion of the orbit, we are not able to find definitive orbit solutions. By using a Monte Carlo search technique we explored the orbital parameter space allowed by the current set of data available for each binary. We constructed weighted distributions for the total mass of the binaries derived from a large sample of possible orbits that fit the data. These mass distributions show that the total mass is already well defined. We compute total mass estimates of 0.78, 0.66, 1.13, and 4.13M_⊙ for DF Tau, ZZ Tau, Elias 12 Na-Nb, and T Tau Sa-Sb, respectively, using a distance of 140 pc. For Elias 12 Na-Nb, where the orbital coverage spans ∼164°, we compute a preliminary orbit solution with a period of ∼9-12 yr. By including an earlier lunar occultation measurement, we also find a likely orbit solution for ZZ Tau with a period of ∼32 yr. With additional measurements to continue mapping the orbits the derived dynamical masses will be useful in constraining the theoretical tracks of pre-main-sequence evolution.

Structural analysis has been performed for a sample of 15 southern early-type disk galaxies, mainly S0 galaxies, using high-resolution K_s-band images. The galaxies are mostly barred, and many of them show multiple structures including bars and ovals, typical for S0 galaxies. The new images are of sufficient quality to reveal new detail of the morphology of the galaxies. For example, we report a hitherto undetected nuclear ring in NGC 1387, a nuclear bar in NGC 1326, and in the residual image a weak primary bar in NGC 1317. For the galaxies we (1) measure the radial profiles of the orientation parameters derived from the elliptical isophotes, (2) apply Fourier methods for calculating tangential forces, and, in particular, (3) apply structural decomposition methods. For galaxies with multiple structures a two-dimensional method is found to be superior to a one-dimensional method but only if in addition to the bulge and the disk at least one other component is taken into account. We find strong evidence of pseudobulges in S0 galaxies: 10 of the galaxies have a shape parameter of the bulge near n = 2, indicating that the bulges are more disklike than following the R^1/4 law. Also, six of the galaxies have either nuclear rings, nuclear bars, or nuclear disks. In all nonelliptical galaxies in our sample the bulge-to-total (B/T) flux ratio is less than 0.4, as is typically found in galaxies having pseudobulges. In two of the galaxies the B/T flux ratio is as small as in typical Sc-type spiral galaxies. This might be the hitherto undiscovered link in the scenario in which spiral galaxies are transformed into S0 galaxies. Also, bars in S0 systems are found to be shorter and less massive and to have smaller bar torques than bars in S0/a-type galaxies.

Near-infrared observations have been carried out to survey young stellar objects in the second-largest H II region in the Large Magellanic Cloud, N11. A total area of about 700 arcmin² is covered in the J, H, and K_S bands. We selected a total of 559 OB and 127 Herbig Ae/Be star candidates out of the detected sources based on their near-infrared colors and magnitudes. The existence of these young stellar objects indicates that star formation activity is underway in the whole N11 region. Many Herbig Ae/Be star candidates are distributed around the periphery of the OB association LH 9. Spatial correlations of the OB and Herbig Ae/Be star candidates with the objects observed at other wavelengths (optical, radio continuum, Hα, CO, and X-ray) suggest that the birth of the young stellar populations in peripheral molecular clouds was triggered originally by LH 9. It is likely that the trigger for this star formation was an expanding supershell blown by the OB association. In N11 a new generation of stars would have been formed in the clouds developed from swept-up interstellar medium.

We present a drift-scan survey covering a ∼5° × 50° region toward the southern portion of the Taurus-Auriga molecular cloud. Data taken in the B,R,I filters with the Quest-2 camera on the Palomar 48 inch (1.2 m) Samuel Oschin Telescope were combined with Two Micron All Sky Survey near-infrared photometry to select candidate young stars. Follow-up optical spectroscopy of 190 candidates led to the identification of 42 new low-mass pre-main-sequence stars with spectral types M4-M8, of which approximately half exhibit surface gravity signatures similar to known Taurus stars, while the other half exhibit surface gravity signatures similar to members of the somewhat older Upper Scorpius, TW Hya, and β Pic associations. The pre-main-sequence stars are spread over ∼35°, and many are located well outside of previously explored regions. From assessment of the spatial and proper-motion distributions, we argue that the new pre-main-sequence stars identified far from the clouds cannot have originated from the vicinity of the 1-2 Myr old subclusters that contain the bulk of the identified Taurus members but instead represent a newly identified area of recent star formation near the clouds.

We have obtained new mid-infrared observations of 65 Class I/flat-spectrum (FS) objects in the Perseus, Taurus, Chamaeleon I and II, ρ Ophiuchi, and Serpens dark clouds. These objects represent a subset of the young stellar objects (YSOs) from our previous near-infrared multiplicity surveys. We detected 45 out of 48 (94%) of the single sources, 16 out of 16 (100%) of the primary components, and 12 out of 16 (75%) of the secondary/triple components of the binary/multiple objects surveyed. One target, IRS 34, a 031 separation FS binary, remains unresolved at near-infrared wavelengths. The composite spectral energy distributions for all of our sample YSOs are either Class I or FS, and in 15 out of 16 multiple systems at least one of the individual components displays a Class I or FS spectral index. However, the occurrence of mixed pairings, such as FS with Class I, FS with Class II, and, in one case, an FS with a Class III (Cha I T33B), is suprisingly frequent. Such behavior is not consistent with that of multiple systems among T Tauri stars (TTSs), where the companion of a classical TTS also tends to be a classical TTS, although other mixed pairings have been previously observed among Class II YSOs. Based on an analysis of the spectral indices of the individual binary components, there appears to be a higher proportion of mixed Class I/FS systems (65%-80%) than that of mixed classical and weak-lined TTSs (25%-40%), demonstrating that the envelopes of Class I/FS systems are rapidly evolving during this evolutionary phase. In general, the individual binary/multiple components suffer very similar extinctions, A_v, suggesting that most of the line-of-sight material is either in the foreground of the molecular cloud or circumbinary. We report the discovery of a steep spectral index secondary companion to ISO-Cha I 97, detected for the first time via our mid-infrared observations. In our previous near-infrared imaging survey of binary/multiple Class I and FS YSOs, ISO-Cha I 97 appeared to be single. With a spectral index of α ≥ +3.9, the secondary component of this system is a member of a rare class of very steep spectral index YSOs, those with α > +3. Only three such objects have previously been reported, all of which are either Class 0 or Class I.

We use techniques from nonparametric function estimation theory to extract the density profiles, and their derivatives, from a set of N-body dark matter halos. We consider halos generated from ΛCDM simulations of gravitational clustering, as well as isolated spherical collapses. The logarithmic density slopes γ ≡ d log ρ/d log r of the ΛCDM halos are found to vary as power laws in radius, reaching values of γ ≈ -1 at the innermost resolved radii, ∼10^-2r_vir. This behavior is significantly different from that of broken-power-law models like the Navarro-Frenk-White (NFW) profile but similar to that of models like de Vaucouleurs's. Accordingly, we compare the N-body density profiles with various parametric models to find which provide the best fit. We consider an NFW-like model with arbitrary inner slope; Dehnen & McLaughlin's anisotropic model; Einasto's model (identical in functional form to Sérsic's model but fitted to the space density); and the density model of Prugniel & Simien that was designed to match the deprojected form of Sérsic's R^1/n law. Overall, the best-fitting model to the ΛCDM halos is Einasto's, although the Prugniel-Simien and Dehnen-McLaughlin models also perform well. With regard to the spherical-collapse halos, both the Prugniel-Simien and Einasto models describe the density profiles well, with an rms scatter some 4 times smaller than that obtained with either the NFW-like model or the three-parameter Dehnen-McLaughlin model. Finally, we confirm recent claims of a systematic variation in profile shape with halo mass.

We have recently shown that both the Prugniel-Simien model and Sérsic's function (hereafter referred to as the Einasto model when applied to internal density profiles) describe simulated dark matter halos better than a Navarro-Frenk-White-like model with an equal number of parameters. Here we provide analytical expressions for the logarithmic slopes of these models and compare them with data from real galaxies. Depending on the Einasto parameters of the dark matter halo, one can expect an extrapolated inner (0.01-1 kpc) logarithmic profile slope ranging from approximately -0.2 to approximately -1.5, with a typical value at 0.1 kpc around -0.7. Application of this (better fitting) model therefore alleviates some of the past disagreement with observations on this issue. In addition, we provide useful expressions for the concentration and assorted scale radii: r_s, r_-2, r_e, R_e, r_vir, and r_max, the radius where the circular velocity profile has its maximum value. We also present the circular velocity profiles and the radial behavior of ρ(r)/σ(r)³ for both the Einasto and Prugniel-Simien models, where σ(r) is the velocity dispersion associated with the density profile ρ(r). We find this representation of the phase-space density profile to be well approximated by a power law with a slope slightly shallower than -2 near r = r_-2.

We have recently shown that the three-parameter density profile model from Prugniel & Simien provides a better fit to simulated galaxy- and cluster-sized dark matter halos than an Navarro-Frenk-White-like model with arbitrary inner profile slope γ (Paper I). By construction, the parameters of the Prugniel-Simien model equate to those of the Sérsic R^1/n function fitted to the projected distribution. Using the Prugniel-Simien model we are therefore able to show that the location of simulated (10¹²M_⊙) galaxy-sized dark matter halos in the ⟨μ⟩_e- log R_e diagram coincides with that of the brightest cluster galaxies, i.e.; the dark matter halos appear consistent with the Kormendy relation defined by luminous elliptical galaxies. These objects are also seen to define the new, and equally important, relation log(ρ_e) = 0.5 - 2.5 log(R_e), in which ρ_e is the internal density at r = R_e. Simulated (10^14.5M_⊙) cluster-sized dark matter halos and the gas component of real galaxy clusters follow the relation log(ρ_e) = 2.5[1 - log(R_e)]. Given the shapes of the various density profiles, we are able to conclude that while dwarf elliptical galaxies and galaxy clusters can have dark matter halos with effective radii of comparable size to the effective radii of their baryonic component, luminous elliptical galaxies cannot. For increasingly large elliptical galaxies, with increasingly large profile shapes n, to be dark-matter-dominated at large radii requires dark matter halos with increasingly large effective radii compared to the effective radii of their stellar components.

During the past decade η Car has brightened markedly, possibly indicating a change of state. Here we summarize photometry gathered by the Hubble Space Telescope (HST) as part of the HST Treasury Project on this object. Our data include Space Telescope Imaging Spectrograph (STIS) CCD acquisition images, Advanced Camera for Surveys HRC images in four filters, and synthetic photometry in flux-calibrated STIS spectra. The HST's spatial resolution allows us to examine the central star separate from the bright circumstellar ejecta. Its apparent brightness continued to increase briskly during 2002-2006, especially after the mid-2003 spectroscopic event. If this trend continues, the central star will soon become brighter than its ejecta, quite different from the state that existed only a few years ago. One precedent may be the rapid change observed in 1938-1953. We conjecture that the star's mass-loss rate has been decreasing throughout the past century.

Accurate distances to galaxies can be determined from the luminosities of stars at the tip of the red giant branch (TRGB). We use a maximum likelihood algorithm to locate the TRGB in galaxy color-magnitude diagrams. The algorithm is optimized by introducing reliable photometric errors and a completeness characterization determined with artificial star experiments. The program is extensively tested using Monte Carlo simulations, artificial galaxies, and a sample of nearby dwarf galaxies observed with the Hubble Space Telescope WFPC2 and ACS. Our procedure is shown to be reliable, to have good accuracy, and to not introduce any systematic errors. The methodology is especially useful in cases in which the TRGB approaches the photometric limit and/or the RGB is poorly populated.

In the latest in our series of papers on XMM-Newton and ground-based optical follow-up of new candidate magnetic cataclysmic variables (mCVs) found in the Sloan Digital Sky Survey, we report classifications of three systems: SDSS J144659.95+025330.3, SDSS J205017.84-053626.8, and SDSS J210131.26+105251.5. Both the X-ray and optical fluxes of SDSS J1446+02 are modulated on a period of 48.7 ± 0.5 minutes, with the X-ray modulation showing the characteristic energy dependence of photoelectric absorption seen in many intermediate polars (IP). A longer period modulation and radial velocity variation is also seen at around 4 hr, although neither data set is long enough to constrain this longer, likely orbital, period well. SDSS J2050-05 appears to be an example of the most highly magnetized class of mCV, a diskless, stream-fed polar. Its 1.57 hr orbital period is well constrained via optical eclipse timings; in the X-ray it shows both eclipses and an underlying strong, smooth modulation. In this case broadly phase-resolved spectral fits indicate that this change in flux is the result of a varying normalization of the dominant component (a 41 keV MEKAL plasma), plus the addition of a partial covering absorber during the lower flux interval. SDSS J2101+10 is a more perplexing system to categorize: its X-ray and optical fluxes exhibit no large periodic modulations; there are only barely detectable changes in the velocity structure of its optical emission lines; the X-ray spectra require only absorption by the interstellar medium; and the temperatures of the MEKAL fits are low, with maximum temperature components of either 10 or 25 keV. We conclude that SDSS J2101+10 cannot be an IP, nor likely a polar, but is rather most likely a disk accretor—a low-inclination SW Sex star.