Table of contents

An unfortunate problem during the production of this issue resulted in a pagination error. This issue starts on page 2949 instead of following on sequentially from the last page of volume 137, issue 1 (2009 January). Therefore, in this volume, pages 555–2948 do not exist. IOP Publishing sincerely regrets this error.

Kerry KroffePublisher, IOP Publishing

Differential UBV photoelectric photometry for the eclipsing binary MY Cyg is presented. The Wilson–Devinney program is used to simultaneously solve the three light curves together with previously published radial velocities. A comparison is made with the previous solution found with the Russell–Merrill method. We examine the long-term apsidal motion of this well-detached, slightly eccentric system. We determine absolute dimensions, discuss metallicity/Am-star issues, and estimate the evolutionary status of the stars.

We present interferometric+single-dish images, constructed from the Green Bank Telescope (GBT) and VLA observations, of the supernova remnant SN 1006. The image was created using a Multiscale CLEAN algorithm in conjunction with a novel approach for correcting the effect of the non-coplanar baselines. We demonstrate that integrating with a single dish to the confusion limit of the highest resolution interferometric element is not required. Instead, the noise in the map is limited by the signal-to-noise ratio in each observation. The noise in the combined map at the full resolution is dominated by uncertainties in the VLA data, not by uncertainties in our short GBT observation. The resulting image is a significant improvement over images missing short spacing information, and paves the way for future joint GBT+VLA proposals that need to accurately image objects ranging from galaxies to H ii regions.

We present new Keck II NIRSPEC high-spectral resolution 2 μm echelle observations of the young eruptive variable star V1647 Orionis. This star went into outburst in late 2003 and faded to its pre-outburst brightness after approximately 26 months. V1647 Orionis is the illuminating star of McNeil's Nebula and is located near M 78 in the Lynds 1630 dark cloud. Our spectra have a resolving power of approximately 18,000 and allow us to study in detail the weak absorption features present on the strong near-IR veiled continuum. An analysis of the echelle orders containing Mg i (2.1066 μm) and Al i (2.1099 μm), Brγ (2.1661 μm), the Na i doublet (2.206 and 2.209 μm), and the CO overtone bandhead (2.2935 μm) gives us considerable information on the physical and geometric characteristics of the regions producing these spectral features. We find that, at high spectral resolution, V1647 Orionis in quiescence resembles a significant number of FU Orionis type eruptive variables and does not appear similar to the quiescent EX Lupi variables observed. This correspondence is discussed and implications for the evolutionary state of the star are considered.

We present the complete galaxy cluster catalog from the Northern Sky Optical Cluster Survey, a new, objectively defined catalog of candidate galaxy clusters at z ≲ 0.25 drawn from the Digitized Second Palomar Observatory Sky Survey (DPOSS). The data presented here cover the Southern Galactic Cap, as well as the less well-calibrated regions of the Northern Galactic Cap. In addition, due to improvements in our cluster finder and measurement methods, we provide an updated catalog for the well-calibrated Northern Galactic Cap region previously published in Paper II. The complete survey covers 11,411 deg², with over 15,000 candidate clusters. We discuss improved photometric redshifts, richnesses, and optical luminosities which are provided for each cluster. A variety of substructure measures are computed for a subset of over 11,000 clusters. We also discuss the derivation of dynamical radii r₂₀₀ and its relation to cluster richness. A number of consistency checks between the three areas of the survey are also presented, demonstrating the homogeneity of the catalog over disjoint sky areas. We perform extensive comparisons to existing optically and X-ray-selected cluster catalogs, and derive new X-ray luminosities and temperatures for a subset of our clusters. We find that the optical and X-ray luminosities are well correlated, even using relatively shallow ROSAT All Sky Survey and DPOSS data. This survey provides a good comparison sample to the MaxBCG catalog based on Sloan Digital Sky Survey Data, and complements that survey at low redshifts 0.07 < z < 0.1.

We present an analysis of an occulting galaxy pair, serendipitously discovered in the ACS Nearby Galaxy Survey Treasury observations of NGC 253 taken with the Hubble Space Telescope's (HST) Advanced Camera for Surveys in F475W, F606W, and F814W (SDSS − g, broad V, and I). The foreground disk system (at z ⩽ 0.06) shows a dusty disk much more extended than the starlight, with spiral lanes seen in extinction out to 1.5 R₂₅, approximately 6 half-light radii. This pair is the first where extinction can be mapped reliably out to this distance from the center. The spiral arms of the extended dust disk show typical extinction values of A_F475W ∼ 0.25, A_F606W ∼ 0.25, and A_F814W ∼ 0.15. The extinction law inferred from these measures is similar to that of the local Milky Way, and we show that the smoothing effects of sampling at limited spatial resolution (<57 pc, in these data) flattens the observed function through mixing of regions with different extinction. This galaxy illustrates the diversity of dust distributions in spirals, and the limitations of adopting a single dust model for optically similar galaxies. The ideal geometry of this pair of overlapping galaxies and the high sampling of HST data make this data set ideal to analyze this pair with three separate approaches to overlapping galaxies: (1) a combined fit, rotating copies of both galaxies, (2) a simple flip of the background image, and (3) an estimate of the original fluxes for the individual galaxies based on reconstructions of their proper isophotes. We conclude that in the case of high-quality data such as these, isophotal models are to be preferred.

An order of magnitude more dwarf galaxies are expected to inhabit the Local Group, based on currently accepted galaxy formation models, than have been observed. This discrepancy has been noted in environments ranging from the field to rich clusters. However, no complete census of dwarf galaxies exists in any environment. The discovery of the smallest and faintest dwarfs is hampered by the limitations in detecting such faint and low surface brightness galaxies. An even greater difficulty is establishing distances to, or group/cluster membership for, such faint galaxies. The M81 Group provides an almost unique opportunity for establishing membership for galaxies in a low-density region complete to magnitudes as faint as $M_{r^{\prime }} = -10$. With a distance modulus of 27.8, the tip of the red giant branch just resolves in ground-based surveys. We have surveyed a 65 deg² region around M81 with Canada-France-Hawaii Telescope/MegaCam. From these images, we have detected 22 new dwarf galaxy candidates. Photometric, morphological, and structural properties are presented for the candidates. The group luminosity function has a faint-end slope characterized by the parameter α = −1.27 ± 0.06. We discuss implications of this dwarf galaxy population for cosmological models.

The results of an Hα photometric survey of 30 dwarf galaxies of various morphologies in the Centaurus A and Sculptor groups are presented. Of these 30, emission was detected in 13: eight are of late-type, two are early-type, and three are of mixed morphologies. The typical flux detection limit of ∼2 × 10⁻¹⁶ erg s⁻¹ cm⁻² translates into a star-formation rate (SFR) detection limit of 4 × 10⁻⁶M_☉ yr⁻¹. In light of these results, the morphology–density relation is re-examined, and it is shown that, despite a number of unaccounted parameters, there are significant correlations between the factors determining the morphological type of a galaxy and its environment. Dwarf galaxies in high-density regions have a lower current SFR and lower neutral gas content than their low-density counterparts, confirming earlier results from the Local Group and other denser environments. The effect of environment is also seen in the timescale formed from the ratio of blue luminosity to current SFR—dwarfs in higher-density environments have larger values, indicating relatively higher past average SFR. The influence of environment extends very far, and no dwarfs from our sample can be identified as "field" objects.

Many early-type galaxies have been detected at wavelengths of 24–160 μm but the emission is usually dominated by heating from an active galactic nucleus or from the evolved stellar population. Here, we present Spitzer MIPS observations of a sample of elliptical and lenticular galaxies that are rich in cold molecular gas, and we investigate whether the mid-IR to far-IR (FIR) emission could be associated with star formation activity. The 24 μm images show a rich variety of structures, including nuclear point sources, rings, disks, and smooth extended emission. Comparisons to matched-resolution CO and radio continuum images suggest that the bulk of the 24 μm emission can be traced to star formation with some notable exceptions. The 24 μm luminosities of the CO-rich galaxies are typically a factor of 15 larger than what would be expected from the dust associated with their evolved stars. In addition, FIR/radio flux density ratios are consistent with star formation. We conclude that the star formation rates in z = 0 elliptical and lenticular galaxies, as inferred by other authors from UV and optical data, are roughly consistent with the molecular gas abundances and that the molecular gas is usually unstable to star formation activity.

By combining test-particle and self-consistent techniques, we have developed a method to rapidly explore the parameter space of galactic encounters. Our method, implemented in an interactive graphics program³, can be used to find the parameters required to reproduce the observed morphology and kinematics of interacting disk galaxies. We test this system on an artificial data set of 36 equal-mass merging encounters, and show that it is usually possible to reproduce the morphology and kinematics of these encounters and that a good match strongly constrains the encounter parameters.

We present deep composite luminosity functions (LFs) in B, g, V, r, i, and z for six clusters at 0.14 < z < 0.40 observed with the Hubble Space Telescope Advanced Camera for Surveys. The LFs reach to an absolute magnitude of ∼−14 + 5log h mag and are well fitted by a single Schechter function with M*_BgVriz = −19.8, − 20.9 − 21.9, − 22.0, − 21.7, − 22.3 mag, respectively, and α ∼ −1.3 (in all bands). The observations suggest that the galaxy LF is dominated by objects on the red sequence to at least 6 mag below the L* point. Comparison with local data shows that the red sequence is well established at least at z ∼ 0.3 down to ∼ 1/600th of the luminosity of the Milky Way and that galaxies down to the regime of dwarf spheroidals have been completely assembled in clusters at this redshift. We do not detect a steepening of the LF at M > − 16, as is locally observed. If the faint-end upturn is real, the steepening of the LF must be due to a newly infalling population of faint dwarf galaxies.

We present spectroscopic data for individual stars observed from 2004 March through 2008 August as part of our Michigan/MIKE Fiber System (MMFS) survey of four dwarf spheroidal (dSph) galaxies: Carina, Fornax, Sculptor, and Sextans. Using MMFS at the Magellan/Clay Telescope at Las Campanas Observatory, we have acquired 8855 spectra from 7103 red-giant candidates in these Galactic satellites. We list measurements of each star's line-of-sight velocity (median error ±2.1 km s⁻¹) and spectral line indices for iron and magnesium absorption features. We use globular cluster spectra to calibrate the indices onto standard [Fe/H] metallicity scales, but comparison of the resulting metallicities with published values suggests that the MMFS indices are best used as indicators of relative, not absolute, metallicity. The empirical distributions of velocity and spectral indices also allow us to quantify the amount of contamination by foreground stars. In a companion paper, we develop an algorithm that evaluates the membership probability for each star, showing that the present MMFS sample contains more than 5000 dSph members, including 774 Carina members, 2483 Fornax members, 1365 Sculptor members, and 441 Sextans members.

We develop an algorithm for estimating parameters of a distribution sampled with contamination. We employ a statistical technique known as "expectation maximization" (EM). Given models for both member and contaminant populations, the EM algorithm iteratively evaluates the membership probability of each discrete data point, then uses those probabilities to update parameter estimates for member and contaminant distributions. The EM approach has wide applicability to the analysis of astronomical data. Here we tailor an EM algorithm to operate on spectroscopic samples obtained with the Michigan-MIKE Fiber System (MMFS) as part of our Magellan survey of stellar radial velocities in nearby dwarf spheroidal (dSph) galaxies. These samples, to be presented in a companion paper, contain discrete measurements of line-of-sight velocity, projected position, and pseudo-equivalent width of the Mg-triplet feature, for ∼1000–2500 stars per dSph, including some fraction of contamination by foreground Milky Way stars. The EM algorithm uses all of the available data to quantify dSph and contaminant distributions. For distributions (e.g., velocity and Mg-index of dSph stars) assumed to be Gaussian, the EM algorithm returns maximum-likelihood estimates of the mean and variance, as well as the probability that each star is a dSph member. These probabilities can serve as weights in subsequent analyses. Applied to our MMFS data, the EM algorithm identifies more than 5000 stars as probable dSph members. We test the performance of the EM algorithm on simulated data sets that represent a range of sample size, level of contamination, and amount of overlap between dSph and contaminant velocity distributions. The simulations establish that for samples ranging from large (N ∼ 3000, characteristic of the MMFS samples) to small (N ∼ 30), resembling new samples for extremely faint dSphs), the EM algorithm distinguishes members from contaminants and returns accurate parameter estimates much more reliably than conventional methods of contaminant removal (e.g., sigma clipping).

We present initial results and source lists of variable sources in the Large Magellanic Cloud (LMC) for which we detect thermal infrared variability from the Surveying the Agents of a Galaxy's Evolution (SAGE) survey, which had two epochs of photometry separated by 3 months. The SAGE survey mapped a 7° × 7° region of the LMC using the Infrared Array Camera (IRAC) and the MIPS instruments on board Spitzer. Variable sources are identified using a combination of the IRAC 3.6, 4.5, 5.8, 8.0 μ bands and the MIPS 24 μ bands. An error-weighted flux difference between the two epochs is used to assess the variability. Of the ∼3 million sources detected at both epochs, we find ∼2000 variable sources for which we provide electronic catalogs. Most of the variable sources can be classified as asymptotic giant branch (AGB) stars. A large fraction (>66%) of the extreme AGB stars are variable and only smaller fractions of carbon-rich (6.1%) and oxygen-rich (2.0%) stars are detected as variable sources. We also detect a population of variable young stellar object candidates.

We present the results of wide-field JHK_S polarimetry toward the H ii region S106 using the Infrared Survey Facility telescope. Our polarimetry data revealed an extended (up to ∼5') polarized nebula over S106. We confirmed the position of the illuminating source of most of the nebula as consistent with S106 IRS 4 through an analysis of polarization vectors. The bright portion of the polarized intensity is consistent with the red wing component of the molecular gas. Diffuse polarized intensity emission is distributed along the north–south molecular gas lanes. We found the interaction region between the radiation from S106 IRS 4 and the dense gas. In addition, we also discovered two small polarization nebulae, SIRN 1 and SIRN 2, associated with a young stellar object (YSO). Aperture polarimetry of point-like sources in this region was carried out for the first time. The regional magnetic field structures were derived using point-like source aperture polarimetry, and the magnetic field structure position angle around the cluster region in S106 was found to be ∼120°. The magnetic fields in the cluster region, however, have three types of position angles: ∼20°, ∼80°, and ∼120°. The present magnetic field structures are consistent with results obtained by submillimeter continuum observations. We found that the magnetic field direction in the dense gas region is not consistent with that of the low-density gas region.

We present a study of the spectral, polarimetric, morphological, and environmental properties of the diffuse radio source 0809+39 using observations taken with the Westerbork Synthesis Radio Telescope, the Very Large Array, and archival optical and X-ray data. The source has two distinct diffuse, steep-spectrum components, one in the north that is highly polarized, and a linear southern component undetected in polarization. We discuss several plausible origins for each component, and conclude that the northern bright polarized component is most likely a radio relic associated with a poor z ∼ 0.2 cluster of galaxies, with a radio/X-ray luminosity ratio two orders of magnitude above typical values. The southern component is aligned with a more extended filament of galaxies ∼5 Mpc long at z ∼ 0.04. Deep optical and X-ray follow-ups are still needed in order to confirm and understand the physical origins of the synchrotron emission. Whatever the details of these origins, 0809+39 highlights the utility of synchrotron radiation for illuminating the diffuse components of low density environments unrelated to rich clusters.

When the Wide Field Camera 3 (WFC3) is installed on the Hubble Space Telescope (HST), the astronomical community will have access to powerful new capabilities for investigating resolved stellar populations. The WFC3 Galactic Bulge Treasury program will obtain deep imaging in five photometric bands on four low-extinction fields. These data will have no proprietary period, and will enable a variety of science investigations not possible with previous data sets. To aid in planning for the use of these data and for future observing proposals, we provide an introduction to the Treasury program, its photometric system, and the associated calibration effort.

The observing strategy is based upon a new photometric system employing five WFC3 bands spanning the UV, optical, and near-infrared: F390W, F555W, F814W, F110W, and F160W (analogous but not identical to the ground-based filters Washington C, V, I, J, and H). With these bands, one can construct reddening-free indices of temperature and metallicity. Using this photometric system, the program will target six fields in well studied star clusters, spanning a wide range of metallicity, and four fields in low-extinction windows of the Galactic bulge. The cluster data serve to calibrate the reddening-free indices, provide empirical population templates, and correct the transformation of theoretical isochrone libraries into the WFC3 photometric system. The bulge data will shed light on the bulge formation history, and will also serve as empirical population templates for other studies. One of the fields includes 12 candidate hosts of extrasolar planets.

Color–magnitude diagrams (CMDs) are the most popular tool for analyzing resolved stellar populations. However, due to degeneracies among temperature, metallicity, and reddening in traditional CMDs, it can be difficult to draw robust conclusions from the data. The five-band system used for the bulge Treasury observations will provide reddening-free indices that are roughly orthogonal in temperature and metallicity, and we argue that model fitting in an index–index diagram will make better use of the information than fitting separate CMDs. We provide some results from simulations to show the expected quality of the data and their potential for differentiating between different star formation histories.

For the very short period subdwarf B eclipsing binary HW Vir, we present new CCD photometry made from 2000 through 2008. In order to obtain consistency of the binary parameters, our new light curves, showing sharp eclipses and a striking reflection effect, were analyzed simultaneously with previously published radial velocity data. The secondary star parameters of M₂ = 0.14 M_☉, R₂ = 0.18 R_☉, and T₂ = 3084 K are consistent with those of an M6-7 main-sequence star. A credibility issue regarding bolometric corrections is emphasized. More than 250 times of minimum light, including our 41 timings and spanning more than 24 yr, were used for a period study. From a detailed analysis of the O − C diagram, it emerged that the orbital period of HW Vir has varied as a combination of a downward-opening parabola and two sinusoidal variations, with cycle lengths of P₃ = 15.8 yr and P₄ = 9.1 yr and semiamplitudes of K₃ = 77 s and K₄ = 23 s, respectively. The continuous period decrease with a rate of −8.28 × 10⁻⁹ days yr⁻¹ may be produced by angular momentum loss due to magnetic stellar wind braking but not by gravitational radiation. Of the possible causes of the cyclical components of the period change, apsidal motion and magnetic period modulation can be ruled out. The most reasonable explanation of both cyclical variations is a pair of light-travel-time effects driven by the presence of two substellar companions with projected masses of M₃sin i₃ = 19.2 M_Jup and M₄sin i₄ = 8.5 M_Jup. The two objects are the first circumbinary planets known to have been formed in a protoplanetary disk as well the first ones discovered by using the eclipse-timing method. The detection implies that planets could be common around binary stars just as are planets around single stars and demonstrates that planetary systems formed in a circumbinary disk can survive over long timescales. Depending on the thermal inertia of their massive atmospheres, the hemispheres of the planets turned toward the stars can experience substantial reciprocating temperature changes during the minutes-long primary eclipse intervals.

Spitzer Space Telescope spectra reveal 10 μm silicate emission from circumstellar dust orbiting six externally polluted white dwarfs. Micron-size glasses with an olivine stoichiometry can account for the distinctively broad wings that extend to 12 μm; these particles likely are produced by tidal disruption of asteroids. The absence of infrared polycyclic aromatic hydrocarbon features is consistent with a scenario where extrasolar rocky planets are assembled from carbon-poor solids.

We study the Milky Way region (|Z|< 3.0 kpc) where the thick disk and inner halo overlap by using the kinematics of local blue horizontal branch (BHB) stars (within 1 kpc) and new samples of BHB stars and A-type stars from the Century Survey. We derive Galactic U, V, and W velocities for these BHB and A-type star samples using proper motions from the NOMAD catalog. The mean velocities and the velocity dispersions of the BHB samples (|Z| < 3 kpc) are characteristic of the halo, while those of the Century Survey A-type stars are characteristic of the thick disk. There is no evidence from our samples that the BHB stars rotate with the thick disk in the region |Z| < 3 kpc. Nearly a third of the nearby local RR Lyrae stars have disk kinematics and are more metal rich than [Fe/H] ∼ −1. Only a few percent of the Century Survey BHB (CBHB) stars have these properties. Only one nearby BHB star (HD 130201) is likely to be such a disk star but selection based on high proper motions will have tended to exclude such stars from the local sample. The scale height derived from a sample of local RR Lyrae stars agrees with that of the CBHB stars. The local samples of BHB stars and metal-weak red giants are too incomplete for a similar comparison.

We describe Chandra/ACIS-I observations of the massive ∼ 13–14 Myr-old cluster, h Persei, part of the famous Double Cluster (h and χ Persei) in Perseus. Combining the list of Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ∼ 165 X-ray bright stars with V ≲ 23. Roughly 142 have optical magnitudes and colors consistent with cluster membership. The observed distribution of L_x peaks at L_x ∼ 10^30.3 erg s⁻¹ and likely traces the bright edge of a far larger population of ≈ 0.4–2 M_☉ X-ray active stars. From a short list of X-ray active stars with IRAC 8 μm excess from warm, terrestrial zone dust, we derive a maximum X-ray flux incident on forming terrestrial planets. Although there is no correlation between X-ray activity and IRAC excess, the fractional X-ray luminosity correlates with optical colors and spectral type. By comparing the distribution of L_x/L_⋆ versus spectral type and V − I in h Per with results for other 1–100 Myr-old clusters, we show that stars slightly more massive than the Sun (≳ 1.5 M_☉) fall out of X-ray saturation by ≈ 10–15 Myr. Changes in stellar structure for ≳ 1.5 M_☉ stars likely play an important role in this decline of X-ray emission.

I present results from an optical spectroscopic investigation of the binary system HD 42401 (V1388 Ori; B2.5 IV–V + B3 V). A combined analysis of V-band photometry and radial velocities indicates that the system has an orbital period of 2.18706 ± 0.00005 days and an inclination of 755 ± 02. This solution yields masses and radii of M₁ = 7.42 ± 0.08 M_☉ and R₁ = 5.60 ± 0.04 R_☉ for the primary and M₂ = 5.16 ± 0.03 M_☉ and R₂ = 3.76 ± 0.03 R_☉ for the secondary. Based on the position of the two stars plotted on a theoretical Hertzsprung–Russell diagram, I find that the age of the system is ≳ 25 Myr and that both stars appear overluminous for their masses compared to single-star evolutionary tracks. A fit of the spectral energy distribution based on photometry from the literature yields a distance of 832 ± 89 pc to HD 42401.

We perform a new analysis of the extant ROSAT and XMM-Newton X-ray surveys of the southern open cluster Blanco 1, utilizing new BVI_c photometric and proper motion data sets. In our study, we match optical counterparts to 47 X-ray sources associated with Blanco 1 cluster members, six of which were listed in previous X-ray studies as cluster nonmembers. Our new catalog of optical counterparts to X-ray sources clearly traces out the Blanco 1 main sequence in a color–magnitude diagram, extending from early G to mid-M spectral types. Additionally, we derive new X-ray luminosities as well as ratios of X-ray to bolometric luminosities for confirmed cluster members. We compare these X-ray properties to other young open clusters, including the coeval Pleiades cluster, to investigate the relationship between age and X-ray activity. We find that stars in Blanco 1 generally exhibit X-ray properties similar to those of other open clusters, namely increasing L_x/L_bol with reducing mass for earlier-type stars, and a saturation limit of L_x/L_bol at a magnitude of 10⁻³ for stars with V − I_c ≳ 1.25. More generally, the X-ray detected stars in Blanco 1 have X-ray emission magnitudes that agree with the overall trends seen in the other young clusters. We observe that X-ray emission decays as a function of age and the rate of this decay is mass dependent. Specifically, for higher mass stars, the trend is Skumanich like (i.e., L_x/L_bol ∝ age^−1/2); however, as one goes to lower masses the magnitude of X-ray emission becomes less of a function of age. In fact, for the lowest mass stars (M-type), there is no observable reduction in X-ray production during the first ∼1 Gyr of their lives. However, due to a lack of sensitivity to low X-ray fluxes, there may exist M-type stars that have less than saturated levels of X-ray flux which are not included in our study. In a direct comparison of Blanco 1 to the Pleiades open cluster, members of both clusters have similar X-ray characteristics; however, there does appear to be some discrepancies in the distribution of L_x/L_bol as a function of color that may be related to scatter seen in the Pleiades CMD. Moreover, previous comparisons of this nature for Blanco 1 were not possible due to the reliance on photographic photometry. This is where the power of precise, homogeneous, and standardized CCD photometry allows for a high fidelity, detailed study of the X-ray properties of stars in Blanco 1, as well as a thorough comparison of Blanco 1 to other well-studied open clusters.

Astrophysics is evolving toward a more rational use of costly observational data by intelligently exploiting the large terrestrial and spatial astronomical databases. In this paper, we present a study showing the suitability of an expert system to perform the classification of stellar spectra in the Morgan and Keenan (MK) system. Using the formalism of artificial intelligence for the development of such a system, we propose a rules' base that contains classification criteria and confidence grades, all integrated in an inference engine that emulates human reasoning by means of a hierarchical decision rules tree that also considers the uncertainty factors associated with rules. Our main objective is to illustrate the formulation and development of such a system for an astrophysical classification problem. An extensive spectral database of MK standard spectra has been collected and used as a reference to determine the spectral indexes that are suitable for classification in the MK system. It is shown that by considering 30 spectral indexes and associating them with uncertainty factors, we can find an accurate diagnose in MK types of a particular spectrum. The system was evaluated against the NOAO-INDO-US spectral catalog.

We have used deep optical (Hα and [S ii]) and near-IR (H₂ and K_S) images and catalogs of protostars based on optical and infrared data to follow up our previous observations and examine the protostellar outflow population in the Barnard 1 (B1) dark cloud. The deep images presented here link shocks at the low extinction periphery of the cloud to an outflow system that bisects the confused core of B1. In addition, we find that a deeply embedded infrared shock, previously identified as a protostar, is likely the impact of a flow on a submillimeter clump. In all, we detail nine outflow systems in this cloud, eight of which have clearly identified source protostars.

A few nearby interacting galaxies are known that host elevated numbers of ultraluminous X-ray sources. Here we report the results of a multiwavelength study of the X-ray source population in the field of the interacting pair of galaxies NGC 5774/5775. A total of 49 discrete sources are detected, including 12 ultraluminous X-ray source candidates with luminosities above 10³⁹ erg s⁻¹ in the 0.5–8.0 keV X-ray band. X-ray source positions are mapped onto optical and radio images to search for potential counterparts. Twelve sources in the field have optical counterparts. Optical colors are used to differentiate these sources, which are mostly located outside the optical extent of the interacting galaxies, as potential globular clusters (2), one compact blue dwarf galaxy, and quasars (5). We obtained optical spectra of two of the latter, which confirm that they are background quasars. We expect three background sources in the field of these two galaxies. These results are used to determine the true X-ray population of these two interacting galaxies, which are connected with two bridges. Two high-mass X-ray binaries are detected on these two bridges, suggesting their formation through the interaction-induced star formation episode. NGC 5774 is an extremely low star forming galaxy with five X-ray sources plus three ultraluminous X-ray source candidates. Observed X-ray population of this galaxy does not scale with the star formation rate (SFR) alone but it may scale jointly with the mass of the galaxy and the SFR. Twenty-four X-ray sources (excluding the active galactic nucleus, AGN) are detected in NGC 5775. and its X-ray luminosity function is consistent with that of other interacting galaxies, suggesting that these galaxies have comparable numbers of luminous sources. No X-ray point source was detected at the center of this galaxy to a limiting luminosity of 3 × 10³⁷ erg s⁻¹. Wind/outflow is detected from the central region of NGC 5775. Subsolar diffuse gas with temperature ∼0.31 ± 0.04 keV is present in this galaxy, which suggest that NGC 5775 is in the beginning of the evolutionary process. Twelve ultraluminous X-ray source candidates are detected within the D₂₅ isophotes of NGC 5774/5775. Several of them are highly variable X-ray sources that fall below the detection levels in one of two X-ray observations spaced 15 months apart. Two ultraluminous X-ray sources are located in the halo of NGC 5775 and one of them is hosted in a globular star cluster. Four of the remaining 10 candidates have powerlaw X-ray spectra with photon indices around 1.8 and are extremely luminous with no optical counterparts. One of these four objects is the brightest (∼10⁴¹ erg s⁻¹) with a possible 6.2 hr period and it varied by more than a factor of 500. Two of the rest six ultraluminous X-ray source candidates are having steep-powerlaw X-ray spectra and are embedded in diffuse Hα emission, which are probably ionized nebulae. These nebulae could be due to energetic supernova explosions or to continuous inflation by jets. Rest four ultraluminous X-ray source candidates are flat-powerlaw X-ray sources hosted in either young star clusters or bright star forming complexes. Two of them are radio sources. Finally, we find that the number of ultraluminous X-ray source candidates in interacting/merging galaxies are correlated with the far-infrared, K-band, and UV luminosities of their host galaxies, suggesting that the formation and evolution of ultraluminous X-ray sources depend not only on the SFR but also on the mass of their host galaxies.

The nonlinear stability of the triangular libration point, L₄, when both of the primaries are oblate spheroids as well as sources of radiation has been studied. It is found that L₄ is stable for all mass ratios in the range of linear stability except for three mass ratios depending upon oblateness coefficients and mass reduction factors.

Using the Expanded Very Large Array, we have conducted a search for 22.2 GHz H₂O megamaser emission in the strongly lensed submm galaxy, SMM J16359+6612 at z = 2.517. This object is lensed into three components, and after a correction for magnification is applied to its submm-wavelength flux density, it is typical of the bulk of the high-redshift, submm galaxy population responsible for the 850 μm extragalactic background (S_850 μm∼ 1 mJy). We do not detect any H₂O megamaser emission, but the lensing allows us to place an interesting constraint on the luminosity of any megamasers present, $L_{\rm H_2 O} <$ 5305 L_☉ for an assumed linewidth of 80 km s⁻¹. Because the far-infrared luminosity in submm galaxies is mainly powered by star formation, and very luminous H₂O megamasers are more commonly associated with quasar activity, it could be that blind searches for H₂O megamasers will not be an effective means of determining redshifts for less-luminous members of the submm galaxy population.

We report on our observing program⁴to capture simultaneous spectra of Ca ii and Balmer lines in a sample of nearby M3 dwarfs. Our goal is to investigate the chromospheric temperature structure required to produce these lines at the observed levels. We find a strong positive correlation between instantaneous measurements of Ca ii K and the Balmer lines in active stars, although these lines may not be positively correlated in time-resolved measurements. The relationship between Hα and Ca ii K remains ambiguous for weak and intermediate activity stars, with Hα absorption corresponding to a range of Ca ii K emission. A similar relationship is also observed between Ca ii K and the higher-order Balmer lines. As our sample consists of a single spectral type, correlations between these important chromospheric tracers cannot be ascribed to continuum effects, as suggested by other authors. These data confirm prior nonsimultaneous observations of the Hα line behavior with increasing activity, showing an initial increase in the Hα absorption with increasing Ca ii K emission, prior to Hα filling in and eventually becoming a pure emission line in the most active stars. We also compare our optical measurements with archival UV and X-ray measurements, finding a positive correlation between the chromospheric and coronal emission for both high and intermediate activity stars. We compare our results with previous determinations of the active fraction of low-mass stars, and discuss them in the context of surface inhomogeneity. Lastly, we discuss the application of these data as empirical constraints on new static models of quiescent M dwarf atmospheres.

We analyze photometric data in V and I for the globular cluster (GC) systems in five of the giant ellipticals in the Coma Cluster: NGC 4874, 4881, 4889, 4926, and IC 4051. All of the raw data, from the Hubble Space Telescope Wide Field Planetary Camera 2 Archive, are analyzed in a homogeneous way so that their five cluster systems can be strictly intercompared. We find that the GC luminosity functions are quite similar to one another and reinforce the common nature of the mass distribution of old, massive star clusters in gE galaxies. The globular cluster luminosity function (GCLF) turnover derived from a composite sample of more than 9,000 GCs appears at V = 27.71 ± 0.07 (M_V = −7.3), and our data reach about half a magnitude fainter than the turnover. We find that both a simple Gaussian curve and an evolved Schechter function fit the bright half of the GCLF equally well, though the Coma GCLF is broader and has a higher “cutoff mass” (M_c ∼ 3 × 10⁶ M_☉) than in any of the Virgo giants. These five Coma members exhibit a huge range in GC specific frequency, from a low of S_N ≃ 0.7 for NGC 4881 up to ≃12 for IC 4051 and NGC 4874. No single formation scenario appears able to account for these differences in otherwise similar galaxies and may require carefully prescribed differences in their merger history, gas-free versus gas-rich progenitors, GC formation efficiency, initial density of environment, or tidal harassment within the Coma potential well. The supergiant cD galaxy NGC 4874 has the richest globular cluster system known, probably holding more than 30,000 clusters; its true extent is not yet determined and may extend well out into the Coma potential well. For the three biggest GC systems (NGC 4874, 4889, IC 4051), analysis of the (V − I) color distributions shows that all three populations are dominated by red, metal-rich clusters. Their metallicity distributions also may all have the normal bimodal form, with the two sequences at mean colors 〈V − I〉(blue) ≃0.98 and 〈V − I〉(red) ≃1.15. These values fall along the previously established correlations of mean color with galaxy luminosity. However, the color distributions and relative numbers of metal-rich clusters show intriguing counterexamples to a trend established by Peng and colleagnes for the Virgo galaxies. For the brightest Virgo ellipticals, they find that the red GCs make up only ∼30% of the cluster population, whereas in our similarly luminous Coma galaxies they make up more than half. At the very highest density and most massive regimes represented by the Coma supergiants, formation of metal-rich clusters seems to have been especially favored.

The incidence of dusty debris disks around low- and intermediate-mass stars has been investigated numerous times in order to understand the early stages of planet formation. Most notably, the Infrared Astronomical Satellite (IRAS) mission observed the entire sky at mid- and far-infrared (IR) wavelengths, identifying the first debris disk systems, but was unable to detect a statistically significant sample of warm debris disks due to its limited sensitivity at 12 μm. Using Tycho-2 Spectral Catalog stars previously shown to exhibit 8 μm mid-IR circumstellar excesses confirmed at 24 μm in the Spitzer Galactic Legacy Infrared MidPlane Survey Extraordinaire (GLIMPSE) survey, we investigate the frequency of mid-IR excesses among intermediate-mass (2–4 M_☉) stars in a complete volume-limited sample. Our study of 338 stars is four times larger than a complete sample of 12 μm sources from the IRAS Point Source Catalog. We find that 0.3% ± 0.3% of intermediate-mass stars exhibit a signature of a possible terrestrial-temperature debris disks at wavelengths of 8 μm and greater. We also find that 1.2% ± 0.6% of intermediate-mass stars exhibit evidence for circumstellar disks undergoing inner disk clearing, i.e., candidate transition disk systems. Using stellar lifetimes and the frequency of transition and primordial disks within a given spectral type, we find that pre-main-sequence disks around intermediate-mass stars dissipate in 5 ± 2 Myr, consistent with other studies.

We report on low-resolution (R ≈ 3000) spectropolarimetry of the A0 supergiant star HD 92207. This star is well known for significant spectral variability. The source was observed on seven different nights spanning approximately three months in time. With a rotation period of approximately one year, our data cover approximately a quarter of the star's rotational phase. Variability in the continuum polarization level is observed over this period of time. The polarization across the Hα line on any given night is typically different from the degree and position angle of the polarization in the continuum. Interestingly, Hβ is not in emission and does not show polarimetric variability. We associate the changes at Hα as arising in the wind, which is in accordance with the observed changes in the profile shape and equivalent width of Hα along with the polarimetric variability. For the continuum polarization, we explore a spiral shaped wind density enhancement in the equatorial plane of the star, in keeping with the suggestion of Kaufer et al. Variable polarization signatures across Hα are too complex to be explained by this simple model and will require a more intensive polarimetric follow-up study to interpret properly.

We present an analysis of 23 L dwarfs whose optical spectra display unusual features. Twenty-one were uncovered during our search for nearby, late-type objects using the Two Micron All Sky Survey, while two were identified in the literature. The unusual spectral features, notably weak FeH molecular absorption and weak Na i and K i doublets, are attributable to low gravity and indicate that these L dwarfs are young, low-mass brown dwarfs. We use these data to expand the spectral classification scheme for L0- to L5-type dwarfs to include three gravity classes. Most of the low-gravity L dwarfs have southerly declinations and distance estimates within 60 pc. Their implied youth, on-sky distribution, and distances suggest that they are members of nearby, intermediate-age (∼10–100 Myr), loose associations such as the β Pictoris moving group, the Tucana/Horologium Association, and the AB Doradus moving group. At an age of 30 Myr and with effective temperatures from 1500 to 2400 K, evolutionary models predict masses of 11–30 M_Jupiter for these objects. One object, 2M 0355+11, with J − K_s = 2.52 ± 0.03, is the reddest L dwarf found in the field and its late spectral type and spectral features indicative of a very low gravity suggest it might also be the lowest mass field L dwarf. However, before ages and masses can be confidently adopted for any of these low-gravity L dwarfs, additional kinematic observations are needed to confirm cluster membership.

We present the results of a speckle interferometric survey of Galactic massive stars that complements and expands upon a similar survey made over a decade ago. The speckle observations were made with the Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory 4 m telescopes and USNO speckle camera, and they are sensitive to the detection of binaries in the angular separation regime between 0.″03 and 5″ with relatively bright companions (ΔV < 3). We report on the discovery of companions to 14 OB stars. In total we resolved companions of 41 of 385 O-stars (11%), 4 of 37 Wolf-Rayet stars (11%), and 89 of 139 B-stars (64%; an enriched visual binary sample that we selected for future orbital determinations). We made a statistical analysis of the binary frequency among the subsample that are listed in the Galactic O Star Catalog by compiling published data on other visual companions detected through adaptive optics studies and/or noted in the Washington Double Star Catalog and by collecting published information on radial velocities and spectroscopic binaries. We find that the binary frequency is much higher among O-stars in clusters and associations compared to the numbers for field and runaway O-stars, consistent with predictions for the ejection processes for runaway stars. We present a first orbit for the O-star δ Orionis; a linear solution of the close, apparently optical, companion of the O-star ι Orionis; and an improved orbit of the Be star δ Scorpii. Finally, we list astrometric data for another 249 resolved and 221 unresolved targets that are lower mass stars that we observed for various other science programs.

This paper presents the first observational study of the kinematics of debris from a disrupting globular cluster. Seventy-four bright member candidates of the tidal stream of the cluster Palomar 5, spread over an arc of 8.°5 on the sky, have been observed using high-resolution spectroscopy on the VLT and 17 of them were identified as members of the stream. Their velocities are very close to the radial velocity of the cluster and show a linear trend with position along the stream. We measure the local gradient of the line-of-sight velocity along the stream to be 1.0 ± 0.4 km s⁻¹ deg⁻¹. The stars in the stream show an overall velocity dispersion of 4.7 km s⁻¹, which reduces to only 2.2 km s⁻¹ when removing two stars. This demonstrates that the tidal debris from Pal 5 forms a kinematically cold structure in the Galactic halo, and hence explains the narrowness of the tails. The velocity gradient along the stream provides an important constraint on the orbit of the cluster and thus also on the potential in the Galactic halo. This leads to the conclusion that, in contrast to what was assumed in earlier studies, the cluster's orbit on the sky is not exactly aligned with its tidal tails. A revised model for the orbit of Pal 5 is thus proposed.

We examine the accretion properties in a sample of 42 hard (3–60 keV) X-ray selected nearby broad-line active galactic nuclei (AGNs). The energy range in the sample is harder than that usually used in similar previous studies. These AGNs are mainly complied from the RXTE All Sky Survey, and complemented by the released INTEGRAL AGN catalog. The black hole masses, bolometric luminosities of AGN, and Eddington ratios are derived from their optical spectra in terms of the broad Hβ emission line. The tight correlation between the hard X-ray (3–20 keV) and bolometric/line luminosity is well identified in our sample. Also identified is a strong inverse Baldwin relationship of the Hβ emission line. In addition, all of these hard X-ray AGNs are biased toward luminous objects with a high Eddington ratio (mostly between 0.01 and 0.1) and a low column density (<10²² cm⁻²), which is most likely due to the selection effect of the surveys. The hard X-ray luminosity is consequently found to be strongly correlated with the black hole mass. We believe the sample completeness will be improved in the next few years by the ongoing Swift and the International Gamma-Ray Astrophysics Laboratory missions, and by the next advanced missions, such as NuSTAR, Simbol-X, and NeXT. Finally, the correlation between RFe (= optical Fe ii/Hβ) and disk temperature as assessed by T ∝ (L/L_Edd)M⁻¹_BH leads us to suggest that the strength of the Fe ii emission is mainly determined by the shape of the ionizing spectrum.

Calculation of a stellar occultation lightcurve from an assumed refractivity profile involves the integral of the refractivity or its derivatives along the line of sight through an atmosphere. For the general case, normal numerical integration can be time consuming for least-squares fitting with a modest number of free parameters, or for calculation at a fine grid for comparison with local refocusing (“spikes”) in a lightcurve. A new method, based on the Fourier decomposition of the refractivity profile, can rapidly calculate the line-of-sight integrals needed for occultations. The method is formulated for small planets, to be applicable to Pluto and Triton. The Fourier decomposition method may have applicability to a wider range of atmospheric studies.

We present time-resolved near-infrared (J and H) photometry of the extreme Kuiper belt object (136108) Haumea (formerly 2003 EL61) taken to further investigate rotational variability of this object. The new data show that the near-infrared peak-to-peak photometric range is similar to the value at visible wavelengths, Δm_R = 0.30 ± 0.02 mag. Detailed analysis of the new and previous data reveals subtle visible/near-infrared color variations across the surface of Haumea. The color variations are spatially correlated with a previously identified surface region, redder in B − R and darker than the mean surface. Our photometry indicates that the J − H colors of Haumea (J − H = −0.057 ± 0.016 mag) and its brightest satellite Hi'iaka (J − H = −0.399 ± 0.034 mag) are significantly (greater than 9σ) different. The satellite Hi'iaka is unusually blue in J − H, consistent with strong 1.5 μm water-ice absorption. The phase coefficient of Haumea is found to increase monotonically with wavelength in the range 0.4 < λ < 1.3. We compare our findings with other solar system objects and discuss implications regarding the surface of Haumea.

The evolution of the 2006 outburst of the recurrent nova RS Ophiuchi was followed with 12 X-ray grating observations with Chandra and XMM-Newton. We present detailed spectral analyses using two independent approaches. From the best data set, taken on day 13.8 after outburst, we reconstruct the temperature distribution and derive elemental abundances. We find evidence for at least two distinct temperature components on day 13.8 and a reduction of temperature with time. The X-ray flux decreases as a power law, and the power-law index changes from −5/3 to −8/3 around day 70 after outburst. This can be explained by different decay mechanisms for the hot and cool components. The decay of the hot component and the decrease in temperature are consistent with radiative cooling, while the decay of the cool component can be explained by the expansion of the ejecta. We find overabundances of N and of α elements, which could either represent the composition of the secondary that provides the accreted material or that of the ejecta. The N overabundance indicates CNO-cycled material. From comparisons to abundances for the secondary taken from the literature, we conclude that 20%–40% of the observed nitrogen could originate from the outburst. The overabundance of the α elements is not typical for stars of the spectral type of the secondary in the RS Oph system, and white dwarf material might have been mixed into the ejecta. However, no direct measurements of the α elements in the secondary are available, and the continuous accretion may have changed the observable surface composition.

If binaries are common among massive stars, it will have important consequences for the derivation of fundamental properties such as the cluster age, initial mass function, and dynamical mass. Making use of the multiplexing facilities of the Gemini Multi-Object Spectrograph, we were able to investigate the presence of binary stars within the ionizing cluster of 30 Doradus. From a seven-epoch observing campaign at Gemini South we detect a binary candidate rate of about 50%, which is consistent with an intrinsic 100% binary rate among massive stars. We find that single-epoch determinations of the velocity dispersion give values around 30 km s⁻¹. After correcting the global velocity dispersion for the binary orbital motions, the “true” cluster velocity dispersion is 8.3 km s⁻¹. This value implies a virial mass of about 4.5 × 10⁵M_☉ or 8% of the mass calculated using the single-epoch value. The binary corrected virial mass estimate is consistent with photometric mass determinations, thus suggesting that NGC 2070 is a firm candidate for a future globular cluster.

We report an analysis of twins of spectral types F or later in the 9th Catalog of Spectroscopic Binaries (SB9). Twins, the components of binaries with mass ratio within 2% of 1.0, are found among the binaries with primaries of F and G spectral type. They are most prominent among the binaries with periods less than 43 days, a cutoff first identified by Lucy. Within the subsample of binaries with P < 43 days, the twins do not differ from the other binaries in their distributions of periods (median P ∼ 7 days), masses, or orbital eccentricities. Combining the mass-ratio distribution in the SB9 in the mass range 0.6–0.85 M_☉ with that measured by Mazeh et al. for binaries in the Carney–Latham high proper motion survey, we estimate that the frequency of twins in a large sample of spectroscopic binaries is about 3%. Current theoretical understanding indicates that accretion of high specific angular momentum material by a protobinary tends to equalize its masses. We speculate that the excess of twins is produced in those star-forming regions where the accretion processes were able to proceed to completion for a minority of protobinaries. This predicts that the components of a young twin may appear to differ in age and that, in a sample of spectroscopic binaries in a star formation region, the twins are, on average, older than the binaries with mass ratios much smaller than 1.

The absolute diffuse calibration of the Multiband Imaging Photometer for Spitzer (MIPS) 24 μm channel is investigated by analysis of a sample of H ii regions with a wide range of spatial scales near l = 312°. For each region, sky-subtracted, point-source-subtracted, areally integrated MIPS24 fluxes from the MIPSGAL Legacy program are compared with Midcourse Space Experiment (MSX) 21.3 μm fluxes to determine the flux ratio of MIPS24/MSX 21.3 μm. Spectral energy distributions of these regions indicate that the diffuse calibration of MIPS24 is consistent to within 3% (1σ) with the absolutely validated calibration of MSX.