Table of contents

As an extension of the method by Bahcall and coworkers to investigate the time dependence of the fine-structure constant, we describe an approach based on new observations of forbidden-line multiplets from different ionic species. We obtain optical spectra of fine-structure transitions in [Ne III], [Ne V], [O III], [O I], and [S II] multiplets from a sample of 14 Seyfert 1.5 galaxies in the low-z range 0.035 < z < 0.281. Each source and each multiplet is independently analyzed to ascertain possible errors. Averaging over our sample, we obtain a conservative value α²(t)/α²(0) = 1.0030 ± 0.0014. However, our sample is limited in size and our fitting technique simplistic, as we primarily intend to illustrate the scope and strength of emission-line studies of the time variation of the fine-structure constant. The approach can be further extended and generalized to a "many-multiplet emission-line method" analogous in principle to the corresponding method using absorption lines. With that aim, we note that the theoretical limits on emission-line ratios of selected ions are precisely known and provide well-constrained selection criteria. We also discuss several other forbidden and allowed lines that may constitute the basis for a more rigorous study using high-resolution instruments on the next generation of 8 m class telescopes.

We present the third edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog. The catalog consists of the 46,420 objects in the SDSS Third Data Release that have luminosities larger than M_i = -22 (in a cosmology with H₀ = 70 km s^-1 Mpc^-1, Ω_M = 0.3, and Ω_Λ = 0.7), have at least one emission line with FWHM larger than 1000 km s^-1 or are unambiguously broad absorption line quasars, are fainter than i = 15.0, and have highly reliable redshifts. The area covered by the catalog is ≈4188 deg². The quasar redshifts range from 0.08 to 5.41, with a median value of 1.47; the high-redshift sample includes 520 quasars at redshifts greater than 4, of which 17 are at redshifts greater than 5. For each object the catalog presents positions accurate to better than 02 rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800–9200 Å at a spectral resolution of ≃2000; the spectra can be retrieved from the public database using the information provided in the catalog. A total of 44,221 objects in the catalog were discovered by the SDSS; 28,400 of the SDSS discoveries are reported here for the first time.

The [O III] λ5007 line is commonly used as an indicator of the systemic redshift of active galactic nuclei (AGNs). Also, recent studies have used the width of this emission line as a proxy for the stellar velocity dispersion in the host galaxy. This paper calls both of these assumptions into question by analyzing a sample of approximately 400 AGN spectra from the first data release of the Sloan Digital Sky Survey. These spectra show that the low-ionization forbidden lines ([O II], [N II], and [S II]) define a consistent redshift but that the peak of the [O III] line is blueshifted in approximately half of the AGNs with respect to that redshift. For the sample studied here, the average shift is 40 km s^-1, with the largest shift being more than 400 km s^-1. The magnitude of this shift is found to be correlated with a number of properties, including the width of the [O III] line and the Eddington ratio (L/L_Edd), derived from the luminosity and width of Hβ.

Using a sample of 228 optically selected active galactic nuclei (AGNs) in the 0.01–6.3 redshift range with a high fraction of X-ray detections (81%–86%), we study the relation between rest-frame UV and soft X-ray emission and its evolution with cosmic time. The majority of the AGNs in our sample (155 objects) have been selected from the Sloan Digital Sky Survey (SDSS) in an unbiased way, rendering the sample results representative of all SDSS AGNs. The addition of two heterogeneous samples of 36 high-redshift and 37 low-redshift AGNs further supports and extends our conclusions. We confirm that the X-ray emission from AGNs is correlated with their UV emission and that the ratio of the monochromatic luminosity emitted at 2 keV compared to 2500 Å decreases with increasing luminosity (α_ox = -0.136l_UV + 2.616, where l_UV is in log units) but does not change with cosmic time. These results apply to intrinsic AGN emission, as we correct or control for the effects of the host galaxy, UV/X-ray absorption, and any X-ray emission associated with radio emission in AGNs. We investigate a variety of systematic errors and can thereby state with confidence that (1) the α_ox-l_UV anticorrelation is real and not a result of accumulated systematic errors and (2) any α_ox dependence on redshift is negligible in comparison. We provide the best quantification of the α_ox-l_UV relation to date for normal radio-quiet AGNs; this should be of utility for researchers pursuing a variety of studies.

The Gemini Near Infrared Spectrograph on Gemini South unlocks new possibilities to study the central black holes (BHs) in dusty galaxies that have been inaccessible to previous BH studies. We exploit good near-infrared seeing to measure the central BH of Centaurus A (NGC 5128). We measure the stellar kinematics of NGC 5128 using the region around the CO band heads at 2.3 μm and determine the BH mass using axisymmetric orbit-based models. BHs are believed to be essential components of galaxies, and their evolutionary states appear to be closely linked to those of their hosts. Our current knowledge does not go much beyond this; galaxies such as NGC 5128 (a recent merger with an active galactic nucleus) can further develop this knowledge. However, NGC 5128 and galaxies like it contain large amounts of dust, which hamper optical spectroscopy, making near-infrared measurements an attractive alternative. We find a BH mass of 2.4 × 10⁸M_⊙ for an edge-on model, 1.8 × 10⁸M_⊙ for a model with an inclination of 45°, and 1.5 × 10⁸M_⊙ for a model with an inclination of 20°. We adopt the value for the edge-on model, since it has significantly lower χ²; however, it is unlikely that we can constrain the actual inclination of moderately triaxial NGC 5128 using an axisymmetric modeling procedure. These estimates, based on adjusting the asymmetric kinematics of NGC 5128 so that we can use an axisymmetric code, are consistent with the range of acceptable BH masses implied by a previous gas dynamical study. However, these estimates are 5–10 times higher than that predicted by the correlation between BH mass and velocity dispersion. If NGC 5128 will eventually follow the trend for quiescent galaxies, this result suggests that its BH assembled first before its host component. NGC 5128 thus provides an important example for our knowledge of central BHs; this technique can be applied to other such galaxies to further explore this question.

Assuming that the observed gamma-ray burst (GRB) rate as a function of redshift is proportional to the corrected star formation rate, we derive the empirical distribution of the viewing angles of long BATSE GRBs, P^em(θ), and the distribution of these bursts in the (θ, z)-plane, P^em(θ, z), by using a tight correlation between the collimation-corrected gamma-ray energy (E_γ) and the peak energy of the νF_ν spectrum measured in the rest frame (E). Our results show that P^em(θ) is well fitted by a lognormal distribution centered at log = -0.76 with a width of σ_{log θ} = 0.57. We test different universal structured jet models by comparing model predictions, P^th(θ) and P^th(θ, z), with our empirical results. To make the comparisons reasonable, an "effective" threshold, which corresponds to the sample selection criteria of the long GRB sample, is used. We find that (1) P^th(θ) predicted by a power-law jet model is consistent with P^em(θ), but P^th(θ, z) predicted by this model is significantly different from P^em(θ, z); (2) P^th(θ, z) predicted by a single-Gaussian jet model is more consistent with P^em(θ, z) than that predicted by the power-law jet model, but P^th(θ) predicted by this model rapidly drops at θ > 0.3 rad and greatly deviates from P^em(θ); and (3) both the P^th(θ) and P^th(θ, z) predicted by a two-Gaussian jet model are roughly consistent with our empirical results. A brief discussion shows that cosmological effects on the E_γ-E relation do not significantly affect our results, but sample selection effects on this relationship might significantly influence our results.

In this paper we present an objectively defined catalog of 459 small, high-density groups of galaxies out to z ∼ 0.2 in a region of ∼6260 deg² in the northern sky derived from the Digitized Second Palomar Observatory Sky Survey. Our catalog extends down to r = 19.0 and has a median redshift of z_med = 0.12, making it complementary to Hickson's catalog for the nearby universe (z_med = 0.03). The depth and angular coverage of this catalog makes it valuable for studies of the general characteristics of small groups of galaxies and how galaxies evolve in and around them. We also examine the relationship between compact groups and large-scale structure.

We present a photometric and spectroscopic study of stellar populations in the X-ray–luminous cluster of galaxies RX J0142.0+2131 at z = 0.280. This paper analyzes the results of high signal-to-noise ratio spectroscopy, as well as g'-, r'-, and i'-band imaging, using the Gemini Multi-Object Spectrograph on Gemini North. Of 43 spectroscopic targets, we find 30 cluster members over a range in color. Central velocity dispersions and absorption-line strengths for lines in the range 3700 Å ≲ λ_rest ≲ 5800 Å are derived for cluster members and are compared with a low-redshift sample of cluster galaxies and single stellar population (SSP) models. We use a combination of these indicators to estimate luminosity-weighted mean ages, metallicities ([M/H]), and α-element abundance ratios ([α/Fe]). RX J0142.0+2131 is a relatively poor cluster and lacks galaxies with high central velocity dispersions. Although the red sequence and the Faber-Jackson relation are consistent with pure passive evolution of the early-type population with a formation redshift of z_form ≃ 2, the strengths of the 4000 Å break and scaling relations between metal line indices and velocity dispersion reject this model with high significance. By inverting SSP models for the Hβ_G, Mg b, and ⟨Fe⟩ line indices, we calculate that, at a given velocity dispersion and metallicity, galaxies in RX J0142.0+2131 have luminosity-weighted mean ages 0.14 ± 0.07 dex older than the low-redshift sample. We also find that [α/Fe] in stellar populations in RX J0142.0+2131 is 0.14 ± 0.03 greater than at low redshift. All scaling relations are consistent with these estimated offsets. We speculate that the older luminosity-weighted mean ages and [α/Fe] enhancement can be brought about by a rapidly curtailed burst of star formation in RX J0142.0+2131, such as may be experienced in a cluster-cluster merger. We note that the cluster's velocity dispersion, 1278 ± 134 km s^-1, is larger than expected from both its X-ray luminosity and richness. However, the velocity distribution of galaxies in RX J0142.0+2131 is consistent with being drawn from a Gaussian distribution, and no sign of substructure is found. We conclude that stellar populations in RX J0142.0+2131 cannot evolve into stellar populations similar to those seen in our low-redshift sample through passive evolution. This study provides further evidence that a more complex model, possibly involving ongoing or intermittent star formation and galaxy mergers, is required to describe the evolution of cluster galaxies.

In this paper we analyze the structural parameters of the dwarf galaxies in the Coma Cluster with -18 ≤ M_B ≤ -16 and classify them into two types; those with surface brightness profiles well fitted by a single Sérsic law are called dwarf ellipticals (dEs), and those fitted with Sérsic+exponential profiles are classified as dwarf lenticulars (dS0s). The comparison of the structural parameters of the dwarf galaxies in the Coma and Virgo Clusters shows that they are analogous. Photometrically, the dE and dS0 galaxies in Coma are equivalent, having similar colors and global scales. However, the scale of the innermost parts (bulges) of dS0 galaxies is similar to that of the bulges of late-type spiral galaxies. In contrast, dEs have larger scales than the bulges of bright galaxies. This may indicate that dS0 and dE galaxies have different origins. While dE galaxies can come from dwarf irregulars (dIs) or from processes similar to those that form bright E galaxies, the origin of dS0 galaxies could be harassed bright late-type spiral galaxies.

Spectroscopic observations for 315 emission-line galaxy (ELG) candidates from the KPNO International Spectroscopic Survey (KISS) have been obtained using the MDM Observatory 2.4 m telescope on Kitt Peak. KISS is a wide-field objective-prism survey for extragalactic emission-line objects that has cataloged over 2200 ELG candidates to date. Spectroscopic follow-up observations are being carried out to study the characteristics of the survey objects. The observational data presented here include redshifts, reddening estimates, line equivalent widths, Hα line fluxes, and emission-line ratios. The galaxies have been classified based on their emission-line characteristics. The procedure for selecting the ELG candidates in KISS is found to be very reliable: 93% of the candidates in this sample are verified to have emission lines. A comparison of objective-prism survey data—redshifts, Hα line fluxes, and equivalent widths—to the long-slit measurements shows good overall agreement.

The distribution of bar strengths in disk galaxies is a fundamental property of the galaxy population that has only begun to be explored. We have applied the bar-spiral separation method of Buta and coworkers to derive the distribution of maximum relative gravitational bar torques, Q_b, for 147 spiral galaxies in the statistically well-defined Ohio State University Bright Galaxy Survey (OSUBGS) sample. Our goal is to examine the properties of bars as independently as possible of their associated spirals. We find that the distribution of bar strength declines smoothly with increasing Q_b, with more than 40% of the sample having Q_b ≤ 0.1. In the context of recurrent bar formation, this suggests that strongly barred states are relatively short-lived compared to weakly barred or nonbarred states. We do not find compelling evidence for a bimodal distribution of bar strengths. Instead, the distribution is fairly smooth in the range 0.0 ≤ Q_b < 0.8. Our analysis also provides a first look at spiral strengths Q_s in the OSUBGS sample, based on the same torque indicator. We are able to verify a possible weak correlation between Q_s and Q_b, in the sense that galaxies with the strongest bars tend to also have strong spirals.

As part of our study on the impact of violent star formation on the interstellar medium (ISM) of dwarf galaxies, we report observations of neutral atomic hydrogen (H I) in the starburst dwarf galaxy NGC 1569. High-resolution measurements with the Very Large Array (B, C, and D configuration) are aimed at identifying morphological and kinematical signatures in H I caused by the starburst. Our kinematical data suggest a huge hole in the H I distribution, probably due to the large number of supernovae explosions in the center of the galaxy over the past 20 Myr. Investigating the large-scale H I structure, we confirm the existence of a possible H I companion and a so-called H I bridge east of NGC 1569. Furthermore, we report the detection of additional low-intensity H I halo emission, which leads us to suggest a revised halo structure. On the basis of our new picture, we discuss the origin of the halo gas and possible implications for the evolution of the starburst in NGC 1569.

We present results of a search for supernova remnants (SNRs) in archival Chandra images of M33. We have identified X-ray SNRs by comparing the list of Chandra X-ray sources in M33 with tabulations of SNR candidates identified from (1) elevated [S II]/Hα ratios in the optical and (2) radio spectral indices. In addition, we have searched for optical counterparts to soft sources in the Chandra images and X-ray SNR candidates identified in the XMM-Newton survey of M33. Of the 98 optically known SNRs in M33, 22 have been detected at >3 σ level in the soft band (0.35–1.1 keV). At least four of these SNR candidates are spatially extended based on a comparison of the data to simulated images of point sources. Aside from the optically matching SNRs, we have found one soft X-ray source in M33 that exhibits no optical emission and is coincident with a known radio source. The radio spectral index of this source is consistent with particle acceleration in shocks, leading us to suggest that it is a nonradiative SNR. We have also found new optical counterparts to two soft X-ray SNRs in M33. These counterparts exhibit enhanced [S II]/Hα ratios characteristic of radiative shocks. Pending confirmation from optical spectroscopy, the identification of these two optical counterparts increases the total number of known optically emitting SNRs in M33 to 100. This brings the total number of identified SNRs with X-ray counterparts, including those exclusively detected by the XMM-Newton survey of M33, to 37 SNRs. We find that while there are a similar number of confirmed X-ray SNRs in M33 and the LMC with X-ray luminosities in excess of 10³⁵ ergs s^-1, nearly 40% of the LMC SNRs are brighter than 10³⁶ ergs s^-1, while only 13% of the M33 sample exceed this luminosity. Including X-ray SNR candidates from the XMM-Newton survey (objects lacking optical counterparts) increases the fraction of M33 SNRs brighter than 10³⁶ ergs s^-1 to 22%, still only half the LMC fraction. The differences in luminosity distributions cannot be fully explained by uncertainty in spectral model parameters and are not fully accounted for by abundance differences between the galaxies.

We have studied the properties of a sample of 67 very blue and likely young massive clusters in M31 extracted from the Bologna Revised Catalog of globular clusters, selected according to their color [(B - V)₀ ≤ 0.45] and/or the strength of their Hβ spectral index (Hβ ≥ 3.5 Å). Their existence in M31 has been noted by several authors in the past; we show here that these blue luminous compact clusters (BLCCs) are a significant fraction (≳15%) of the whole globular cluster system of M31. Compared to the global properties of the M31 globular cluster system, they appear to be intrinsically fainter and morphologically less concentrated, with a shallower Balmer jump and enhanced Hβ absorption in their spectra. Empirical comparison with integrated properties of clusters with known ages, as well as with theoretical simple stellar population models, consistently indicates that their typical age is less than ∼2 Gyr, so they are probably not as metal-poor as would be deduced if they were older. When selecting BLCCs by either their (B - V)₀ colors or the strength of their Hβ index, the cluster sample turns out to be distributed on the outskirts of the M31 disk, sharing the kinematic properties of the thin, rapidly rotating disk component. If confirmed to be young and not metal-poor, these clusters indicate the occurrence of significant recent star formation in the thin disk of M31, although they do not set constraints on the epoch of its early formation.

Measurements of the spiral arms (their pitch angle, number, shape, and the interarm separation) in the Milky Way have been published in the period from 1980 to early 2005, using different methods that yielded slightly or widely differing values, depending on hidden or unknown biases. A meta-analysis would be useful for searching for trends among these individual studies. First, we find a convergence for three parameters: the pitch angle, the number of arms, and the shape of the arms. Second, we find a change for the interarm separation near the Sun, a decrease of about 25%; it is our determination of these parameters that evolves, not the actual physical arms. Third, we recalibrate a recent arm model to take account of that gradual change and compare it with the spread in each arm parameter.

Clumps in the solar neighborhood's stellar velocity distribution could be caused by spiral density waves. In the solar neighborhood, stellar velocities corresponding to orbits that are nearly closed in the frame rotating with a spiral pattern represent likely regions for stellar concentrations. Via particle integration, we show that orbits can intersect the solar neighborhood when they are excited by Lindblad resonances with a spiral pattern. We find that a two-armed spiral density wave with pattern speed placing the Sun near the 4:1 inner Lindblad resonance can cause two families of nearly closed orbits in the solar neighborhood. One family corresponds to square-shaped orbits aligned so that their peaks lie on top of, and support, the two dominant stellar arms. The second family corresponds to orbits 45° out of phase with the other family. Such a spiral density pattern could account for two major clumps in the solar neighborhood's velocity distribution. The Pleiades/Hyades moving group corresponds to the first family of orbits, and the Coma Berenices moving group corresponds to the second family. This model requires a spiral pattern speed of approximately 0.66 ± 0.03 times the angular rotation rate of the Sun, or 18.1 ± 0.8 km s^-1 kpc^-1.

Archival data have been combined with recent observations of the Galactic plane using the Very Large Array to create new catalogs of compact centimetric radio sources. The 20 cm source catalog covers a longitude range of -20° < l < 120°; the latitude coverage varies from ±08 to ±27. The total survey area is ∼331 deg²; coverage is 90% complete at a flux density threshold of ∼14 mJy, and over 5000 sources are recorded. The 6 cm catalog covers 43 deg² in the region -10° < l < 42°, |b| < 04 to a 90% completeness threshold of 2.9 mJy; over 2700 sources are found. Both surveys have an angular resolution of ∼6''. These catalogs provide a 30% (at 20 cm) to 50% (at 6 cm) increase in the number of high-reliability compact sources in the Galactic plane, as well as greatly improved astrometry, uniformity, and reliability; they should prove useful for comparison with new mid- and far-infrared surveys of the Milky Way.

We summarize radial velocity studies of selected stars in the old, distant clusters Berkeley 20, Berkeley 21, NGC 2141, Berkeley 29, and Berkeley 31. Cluster members are identified using optical and infrared color-magnitude diagrams, as well as radial velocities derived from high-resolution echelle spectra. Three members of M67 were observed similarly, and those velocities compare extremely well with prior measures. Mean cluster radial velocities are determined. We also employ the highest quality spectra to analyze the chemical compositions of all six clusters for [Fe/H], as well as abundances of α-elements, iron-peak elements, and those synthesized in either the s-process or the r-process. In Be 21 our observed star is found to be rotating rapidly and overabundant in lithium, the second Li-rich star found in this sparse cluster.

We confirm the lack of correlation between abundance and age. For the outer disk, the abundance gradient for [Fe/H] deviates from the trend defined near the solar neighborhood. Rather than declining with increasing galactocentric distance, [Fe/H] appears to reach a "basement" at [Fe/H] ≈ -0.5 beyond R_GC ≈ 10–12 kpc. Our radial abundance distribution for [Fe/H] is not inconsistent with the radial abundance discontinuity exhibited by Cepheids. We find enhanced [O/Fe], [α/Fe], and [Eu/Fe] in the outer disk, revealing a rapid star formation history. The outer disk also exhibits enhancements for s-process elements. We compare the open cluster compositions with those of the thin disk, thick disk, halo, bulge, and dwarf spheroidal galaxies. None of these stellar populations perfectly matches the abundance ratios of the outer disk open clusters. Several key points arise from these comparisons: (1) [O/Fe] and [α/Fe] resemble those of the thick disk. (2) [Na/Fe] and [Al/Fe] are enhanced relative to those of the thin disk. (3) [Ni/Fe] and [Mn/Fe] are in accord with those of the thin disk, while [Co/Fe] may be slightly enhanced. (4) The neutron-capture elements indicate different ratios of s-process to r-process material, with no cluster showing a pure r-process distribution. (5) An unusual pattern exists among the α-elements, with [⟨Mg + Ti⟩/Fe] enhanced while [⟨Si + Ca⟩/Fe] is normal. Similar abundance ratios have been reported for Galactic bulge giants and indicate a common but not necessarily shared nucleosynthetic history between the bulge and the outer disk. Enhanced ratios of [Al/Fe] and [Co/Fe] offer another possible similarity between the bulge and the outer disk.

An intriguing but tentative conclusion is that the outer disk open cluster abundance ratios are consistent with the outer disk being formed via a merger event or series of merger events. The basement in [Fe/H] and enhanced [α/Fe] suggest that the outer disk formed from a reservoir of gas with a star formation history distinct from the solar neighborhood. That the open clusters may be associated with an accreted dwarf galaxy or galaxies is appealing, since the clusters are young and have [α/Fe] ratios indicating a rapid star formation history. However, the high [α/Fe] ratios are unlike those seen in any current dwarf galaxies at the same [Fe/H]. Therefore, the open clusters may have formed as a result of star formation triggered by a merger event or series of mergers in the outer disk. The ages of the outer disk open clusters would then be a measure of when the merger(s) occurred. However, Be 29 is a candidate merger member, while Be 31 is not. One problem with the merger scenario is that open clusters with presumably very different origins have similar and unusual compositions.

Using Hubble Space Telescope Advanced Camera for Surveys Wide Field Channel images, we derive the color-magnitude diagram of the old, metal-rich open cluster NGC 6791 to nearly 29th magnitude in V, which is the neighborhood of the hydrogen-burning limit. Comparison with isochrones leads to a discussion of the distance modulus, the reddening, and the age of the cluster. By making a statistical correction for field stars, we derive a preliminary luminosity function and a very tentative mass function. The white dwarf sequence is clearly shown and has been discussed in a separate paper.

Wide-field BVI photometry and ¹²CO (1 → 0) observations are presented in the region of the open cluster NGC 6520 and the dark molecular cloud Barnard 86. From the analysis of the optical data we find that the cluster is rather compact, with a radius of 10 ± 05, smaller than previous estimates. The cluster age is 150 ± 50 Myr, and the reddening E_B-V = 0.42 ± 0.10. The distance from the Sun is estimated to be 1900 ± 100 pc, which is larger than previous estimates. We finally derive basic properties of the dark nebula Barnard 86 on the assumption that it lies at the same distance as the cluster.

We present Very Large Array (VLA) 3.5 cm continuum observations of the Serpens cloud core. Twenty-two radio continuum sources are detected. Sixteen out of the 22 centimeter sources are suggested to be associated with young stellar objects (Class 0, Class I, flat spectrum, and Class II) of the young Serpens cluster. The rest of the VLA sources are plausibly background objects. Most of the Serpens centimeter sources likely represent thermal radio jets; on the other hand, the radio continuum emission of some sources could be due to a gyrosynchroton mechanism arising from coronally active young stars. The Serpens VLA sources are spatially distributed into two groups; one of them located toward the northwest clump of the Serpens core, where only Class 0 and Class I protostars are found to present centimeter emission, and a second group located toward the southeast clump, where radio continuum sources are associated with objects in evolutionary classes from Class 0 to Class II. This subgrouping is similar to that found in the near-IR, mid-IR, and millimeter wavelength regimes.

We report on high-resolution spectroscopy of four giant stars in the Galactic old open clusters Berkeley 22 and Berkeley 66 obtained with HIRES at the Keck telescope. We find that [Fe/H] = -0.32 ± 0.19 and -0.48 ± 0.24 for Be 22 and Be 66, respectively. Based on these data, we first revise the fundamental parameters of the clusters and then discuss them in the context of the Galactic disk radial abundance gradient. We found that both clusters nicely obey the most updated estimate of the slope of the gradient from the work of Friel and coworkers and are genuine Galactic disk objects.

We present two models for the interstellar extinction in the Galaxy that are based on the hypothesis that the interstellar dust is well mixed with the gas, with a constant ratio (except for a small dependence of metallicity on the Galactic radius), and therefore that the extinction is proportional to the column density of the gas. In the first model we assume that the Galaxy is axisymmetric; the gas density in the disk is a function of the Galactic radius and of the distance perpendicular to the Galactic plane, and the extinction is proportional to the column density of the gas. In the second model we take into account the spiral structure of the Galaxy. In this case, instead of increasing almost linearly with distance, the extinction increases by steps each time a spiral arm is crossed, but only increases slowly in the interarm regions. The gas density distribution is obtained from the Berkeley and Parkes H I surveys and from the Columbia University CO survey. The IRAS 100 μm brightness distribution is also used as a tracer of the interstellar dust column density. The predictions of the models are compared with data taken from a number of catalogs that present color excess and distances for large samples of stars. Our models are useful for estimating distances of objects and color corrections for objects for which the distance can be estimated by some other method, and also for star counts and brightness models of the Galaxy, among other applications.

Worms are defined to be dusty, atomic hydrogen (H I) structures that are observed in low-resolution data to rise perpendicular to the Galactic plane. Data from the 1' resolution Canadian Galactic Plane Survey (CGPS) were systematically searched for narrow vertical H I structures that could be resolved worms. Another motivation for the search was to explore the scenario in which mushroom-shaped worms such as GW 123.4-1.5, studied by English and collaborators, could be generated by a single supernova. However, no other vertical structures of mushroom-shape morphology were found. We also examined objects previously classified as worm candidates by Koo and collaborators; only seven have a significant portion of their structure falling in the CGPS range of l = 74°–147°, -35 < b < +55. Apart from GW 123.4-1.5, we could not confirm that any of these are coherent structures that extend toward the Milky Way's halo. However, a list of 10 narrow vertical structures found in our search is furnished; one structure is ≳500 pc tall, thus extending from the Galactic plane into the halo. We provide details about these narrow vertical structures, including comparisons between H I, radio continuum, IR, and CO observations. Our search was conducted by visual inspection, and we describe the limitations of this approach since it indicates that only six disk-halo features may exist throughout the Milky Way. We also discuss the possible origins of structures at high latitudes and the relationship between mushroom-shaped clouds and old supernova remnants.

Several recent studies of Galactic H I absorption toward background quasars and pulsars have provided evidence that there are opacity changes in the neutral Galactic interstellar medium on size scales as small as a few AU. The nature of these opacity variations has remained a matter of debate but could reflect a variety of physical processes, including changes in the H I spin temperature or gas density. We present three epochs of Very Long Baseline Array (VLBA) observations of Galactic H I absorption toward the quasar 3C 138 with resolutions of 20 mas (∼10 AU). This analysis includes VLBA data from observations in 1999 and 2002 along with a reexamination of the 1995 VLBA data, reported by Faison and coworkers. Improved data reduction and imaging techniques have led to an order of magnitude improvement in sensitivity compared to previous work. With these new data we confirm the previously detected milliarcsecond-scale spatial variations in the H I opacity at the level of Δτ_max = 0.50 ± 0.05. The typical size scale of the optical depth variations is ∼50 mas or 25 AU. In addition, for the first time we see clear evidence for temporal variations in the H I opacity over the 7 yr time span of our three epochs of data. We also attempt to detect the magnetic field strength in the H I gas using the Zeeman effect. From this analysis we have been able to place a 3 σ upper limit on the magnetic field strength per pixel of ∼45 μG. We have also been able to calculate for the first time the plane-of-sky covering fraction of the small-scale H I gas of ∼10%. This small covering fraction suggests that the filling factor of such gas is quite low, in agreement with recent optical observations. We also find that the line widths of the milliarcsecond-scale H I features are comparable to those determined from previous single-dish measurements toward 3C 138, suggesting that the opacity variations cannot be due to changes in the H I spin temperature. From these results we favor a density enhancement interpretation for the small-scale H I structures, although these enhancements appear to be of short duration and are unlikely to be in equilibrium.

We present a survey in the 6₁₆–5₂₃ rotational H₂O transition toward 33 Galactic ultracompact H II regions. Maser emission is detected toward 18 of these sources; two are new detections. High-quality spectra are provided for all 18 sources. We discuss the detection rate of this survey and the correlation of various maser properties with other physical parameters. In addition, we report wide-bandwidth (316 km s^-1), moderate-resolution (∼3'') H₂O maser observations of the HH 80–81 region. We report the first detection of water maser emission at the approximate velocity of the molecular core. This emission is coincident with the extreme tip of the thermal jet and well removed from the much stronger and well-known maser emission at the position of VLA 3.

We explore loose congregations of medium- to high-mass protoclusters identified to the southeast of NGC 2244. On using data from the spatially complete Two Micron All Sky Survey, the true extent of the burst of cluster formation along the ridge of the Rosette Molecular Cloud is revealed. Here we investigate the properties and fine structures of the most prominent cluster embedded in the densest rim of the cloud. This protocluster is resolved into two compact subclusters aligned along the major axis of the entire complex, in line with NGC 2244. The subclusters are found to have a physical scale of around 1 pc, typical of known embedded clusters. The K-band luminosity function also suggests a young age. However, near-infrared excess emission is found in approximately one-sixth of the reddened objects. This is still commensurate with an age estimate of <1 Myr, provided that the massive stars have rapidly stripped the circumstellar material from their neighbors. The well-known massive young binary associated with AFGL 961, however, is situated to the south of the major components of the cluster, where the stellar density is comparatively low. This is inconsistent with mass segregation and signifies a different formation process for these high-mass protostellar objects.

A possible microjet from a low-mass but young star, which has already shed its cocoon, could be rendered observable by the Lyman photon flux in the interior of the Rosette Nebula. Outside this environment it may not have been observable at optical wavelengths. The kinematics of this proposed monopolar microjet from an F8 Ve star have been investigated by spatially resolved, long-slit, spectral observations with the Manchester Echelle Spectrometer on the San Pedro Martir telescope (Mexico). The flow is shown to be approaching to give a radial velocity difference from the host nebula of -56 km s^-1. An outflow velocity of, at the most, a few hundreds of km s^-1 is therefore indicated. If the flow velocity is taken as 200 km s^-1, which is found in other microjets, then this jet's inclination to the sky is ≈16°. The mass in the outflowing ionized gas is estimated from the surface brightness of the Hα emission as ≈6 × 10²⁷ g to give an estimated mass-loss rate of 10^-8 M_⊙ yr^-1, which, along with the detection of the outflow velocity, confirms its microjet identification even though an uncertain filling factor was used in these calculations. The hottest cluster star, which is also in the neighborhood of the microjet, is found alone to emit marginally sufficient Lyman photons to account for the ionization of the jet, although direct observations of the local electron density from optical line ratios are required to confirm this point conclusively.

Fifty-two magnetic white dwarfs have been identified in spectroscopic observations from the Sloan Digital Sky Survey (SDSS) obtained between mid-2002 and the end of 2004, including Data Releases 2 and 3. Although not as numerous or diverse as the discoveries from the first data release, the collection exhibits polar field strengths ranging from 1.5 to ∼1000 MG and includes two new unusual atomic DQA examples, a molecular DQ, and five stars that show hydrogen in fields above 500 MG. The highest field example, SDSS J2346+3853, may be the most strongly magnetic white dwarf yet discovered. Analysis of the photometric data indicates that the magnetic sample spans the same temperature range as for nonmagnetic white dwarfs from the SDSS, and support is found for previous claims that magnetic white dwarfs tend to have larger masses than their nonmagnetic counterparts. A glaring exception to this trend is the apparently low-gravity object SDSS J0933+1022, which may have a history involving a close binary companion.

We present long-term photometry of five magnetic cataclysmic variables (MCVs) that displayed pronounced VY Scl–like low states during the interval 1990–2004. A total of 43 transitions to and from the low states are analyzed and compared with the properties of disk VY Scl transitions from an earlier study. We find that the speeds and shapes of the transitions of both disk and magnetic systems above the CV period gap suggest that the low states are due to starspots on the secondary star drifting in front of the L1 point. For systems below the gap, the characteristics of the transitions point to X-ray irradiation on the L1 point for the cause of the low states. Our results are in accord with the nature of the secondary star, which is expected to be fully convective for systems below the gap. Finally, unresolved flaring events present in the low states of the MCVs in our sample are attributed to activity on the secondary, indicating that these secondaries are indeed chromospherically active.

The radio source FIRST J102347.6+003841 was presented as the first radio-selected cataclysmic variable star. In the discovery paper, Bond et al. (2002) show a spectrum consistent with a magnetic AM Her–type system, or polar, featuring strong Balmer lines, He I and He II emission lines, and a light curve with rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius found a smoothly varying light curve with a period near 4.75 hr and one minimum per orbit, indicating that the state of the system had changed dramatically. We present time-resolved spectra showing a superficially normal, mid-G type photosphere, with no detectable emission lines. The absorption-line radial velocity varies sinusoidally, with semiamplitude 268 ± 4 km s^-1, on the orbital period, which is refined to 0.198094(2) days. At this orbital period, the secondary's spectral type is atypically early, suggesting an unusual evolutionary history. We also obtained photometry around the orbit in B, V, and I. The light curve resembles that observed by Woudt, Warner, and Pretorius, and the colors are modulated in a manner consistent with a heating effect. A simple illumination model matches the observations strikingly well, with a Roche lobe–filling secondary near T_eff = 5650 K being illuminated by a primary with an isotropic luminosity of ∼2 L_⊙. The modest amplitude of the observed modulation constrains the orbital inclination i ∼ 55° or less, unless the gravity darkening is artificially reduced. Combining the low i with the secondary's velocity amplitude gives a primary star mass above the Chandrasekhar limit when conventional gravity darkening is assumed. We consider the robustness of this conclusion and examine the possibility that the compact object in this system is not a white dwarf, in which case this is not actually a cataclysmic variable. On close examination, FIRST J102347.6+003841 defies easy classification.

Radial velocity measurements and sine-curve fits to orbital velocity variations are presented for the ninth set of 10 close binary systems: V395 And, HS Aqr, V449 Aur, FP Boo, SW Lac, KS Peg, IW Per, V592 Per, TU UMi, and FO Vir. The first three are very close, possibly detached, early-type binaries, and all three require further investigation. Particularly interesting is V395 And, whose spectral type is as early as B7/8 for a 0.685 day orbit binary. KS Peg and IW Per are single-line binaries, with the former probably hosting a very low mass star. We have detected a low-mass secondary in an important semidetached system, FO Vir, at q = 0.125 ± 0.005. The contact binary FP Boo is also a very small mass ratio system, q = 0.106 ± 0.005. The other contact binaries in this group are V592 Per, TU UMi, and the well-known SW Lac. V592 Per and TU UMi have bright tertiary companions; for these binaries, and for V395 And, we used a novel technique of arranging the broadening functions into a two-dimensional image in phase. The case of TU UMi turned out to be intractable even using this approach, and we have not been able to derive a firm radial velocity orbit for this binary. Three systems of this group were observed spectroscopically before: HS Aqr, SW Lac, and KS Peg.

Stellar evolution theory predicts that asymptotic giant branch (AGB) stars undergo a series of short thermal pulses that significantly change their luminosity and mass on timescales of hundreds to thousands of years. These pulses are confirmed observationally by the existence of the short-lived radioisotope technetium in the spectra of some of these stars, but other observational consequences of thermal pulses are subtle and may only be detected over many years of observations. Secular changes in these stars resulting from thermal pulses can be detected as measurable changes in period if the star is undergoing Mira pulsations. It is known that a small fraction of Mira variables exhibit large secular period changes, and the detection of these changes among a larger sample of stars could therefore be useful in evolutionary studies of these stars. The American Association of Variable Star Observers (AAVSO) International Database currently contains visual data for over 1500 Mira variables. Light curves for these stars span nearly a century in some cases, making it possible to study the secular evolution of the pulsation behavior on these timescales. In this paper we present the results of our study of period change in 547 Mira variables using data from the AAVSO. We use wavelet analysis to measure the period changes in individual Mira stars over the span of available data. By making linear fits to the period versus time measurements, we determine the average rates of period change, d ln P/dt, for each of these stars. We find nonzero d ln P/dt at the 2 σ significance level in 57 of the 547 stars, at the 3 σ level in 21 stars, and at the level of 6 σ or greater in eight stars. The latter eight stars have been previously noted in the literature, and our derived rates of period change largely agree with published values. The largest and most statistically significant d ln P/dt are consistent with the rates of period change expected during thermal pulses on the AGB. A number of other stars exhibit nonmonotonic period change on decades-long timescales, the cause of which is not yet known. In the majority of stars, the period variations are smaller than our detection threshold, meaning the available data are not sufficient to unambiguously measure slow evolutionary changes in the pulsation period. It is unlikely that more stars with large period changes will be found among heretofore well-observed Mira stars in the short term, but continued monitoring of these and other Mira stars may reveal new and serendipitous candidates in the future.

We have obtained a Hubble Space Telescope STIS ultraviolet high-dispersion echelle-mode spectrum of the binary companion of the double-mode classical Cepheid Y Car. The velocity measured for the hot companion from this spectrum is very different from reasonable predictions for binary motion, implying that the companion is itself a short-period binary. The measured velocity changed by 7 km s^-1 during the 4 days between two segments of the observation, confirming this interpretation. We summarize "binary" Cepheids that are in fact members of a triple system and find that at least 44% are triples. The summary of information on Cepheids with orbits makes it likely that the fraction is underestimated.

New spectroscopic and photometric observations of HD 144110 have been used to obtain an improved orbital element solution and determine some basic properties of the system. This chromospherically active, double-lined spectroscopic binary has an orbital period of 1.6714012 days and a circular orbit. We classify the components as G5 V and K0 V and suggest that they are slightly metal-rich. The photometric observations indicate that the rotation of HD 144110 is synchronous with the orbital period. Despite the short orbital period, no evidence of eclipses is seen in our photometry.

The synchronously rotating G stars in the detached, short-period (0.7 days), partially eclipsing binary ER Vul are the most chromospherically active solar-type stars known. We have monitored activity in the Ca II H and K reversals for almost an entire orbit. Rucinski's broadening function formalism allows the photospheric contribution to be objectively subtracted from the highly blended spectra. The power of the broadening function technique is also demonstrated by the good agreement of radial velocities with those measured by others from less crowded spectral regions. In addition to strong Ca II emission from the primary and secondary, there appears to be a high-velocity stream flowing onto the secondary, where it stimulates a large active region on the surface 30°–40° in advance of the subbinary longitude. A model light curve with a spot centered on the same longitude also gives the best fit to the observed light curve. A flare with ∼13% more power than at other phases was detected in one spectrum. We suggest that ER Vul may offer a magnified view of the more subtle chromospheric effects synchronized to planetary revolution seen in certain 51 Peg–type systems.

The work reported here combines data from the Multichannel Astrometric Photometer (MAP), the European astrometric satellite, Hipparcos, and infrared speckle observations of the nearby subgiant binary star system α Oph. The A5 IV primary is found to have a mass of 2.84 ± 0.19 M_⊙, while the approximately K2 V companion has a mass of 0.78 ± 0.058 M_⊙. The distance modulus is 0.834 ± 0.024 mag, yielding an absolute visual magnitude of 1.248 ± 0.025 mag and an absolute K magnitude of the secondary of 4.3 ± 0.2 mag. Tables list the MAP data and an ephemeris that indicates that the next 4 yr are ideal for further interferometry.

The molecular cloud Barnard 59 is probably an outlier of the Upper Sco/ρ Oph complex. B59 contains several T Tauri stars (TTSs), but outside its northwestern edge are three other Hα-emission objects whose nature has been unclear: IX, KK, and V359 Oph. This paper is a discussion of all three and of a nearby Be star (HD 154851), based largely on Keck HIRES spectrograms obtained in 2004. KK Oph is a close (16) double. The brighter component is an HAeBe star, and the fainter is a K-type TTS. The complex BVR variations of the unresolved pair require both components to be variable. V359 Oph is a conventional TTS. Thus, these pre-main-sequence stars continue to be recognizable as such well outside the boundary of their parent cloud. IX Oph is quite different. Its absorption spectrum is about type G, with many peculiarities: all lines are narrow but abnormally weak, with structures that depend on ion and excitation level and that vary in detail from month to month. It could be a spectroscopic binary of small amplitude. Hα and Hβ are the only prominent emission lines. They are broad, with variable central reversals. However, the most unusual characteristic of IX Oph is the very high (heliocentric) radial velocity: about -310 km s^-1, common to all spectrograms, and very different from the radial velocity of B59, about -7 km s^-1. There is no detectable Li I λ6707 line. There is reason to believe that IX Oph is actually a background object, only aligned with B59. Several conceivable interpretations are discussed: (1) It is unlikely that it is a high-velocity ejectee from the Upper Sco or Upper Cen-Lup associations (the lack of detectable λ6707 shows that it is not the product of a very recent event, and the proper motion points in the wrong direction) or that it was born in or ejected from one of the distant high-velocity CO clouds at this longitude (l = 357°). (2) A stronger possibility is that it is simply a metal-poor high-velocity G- or K-type giant (but such stars are not irregularly variable in light and do not have such strong Balmer emission lines). More likely, (3) IX Oph is a member of the high-velocity, low-metallicity SRd class of semiregular variables found in the field and in some globular clusters. At some phases, those stars show Hα emission like that found in IX Oph and, in one example, emission lines of neutral metals and double absorption lines as in IX Oph.

We present version 1.0 of the NASA Galaxy Evolution Explorer (GALEX) ultraviolet variability (GUVV) catalog, which contains information on 84 time-variable and transient sources gained with simultaneous near-ultraviolet (NUV) and far-ultraviolet (FUV) photometric observations. These time-variable sources were serendipitously revealed in the various 12 diameter star fields currently being surveyed by the GALEX satellite in two ultraviolet bands (NUV 1750–2750 Å, FUV 1350–1750 Å) with limiting AB magnitudes of 23–25. The largest amplitude variable objects currently detected by GALEX are M dwarf flare stars, which can brighten by 5–10 mag in both the NUV and FUV bands during short-duration (<500 s) outbursts. Other types of large-amplitude ultraviolet variable objects include ab-type RR Lyrae stars, which can vary periodically by 2–5 mag in the GALEX FUV band. This first GUVV catalog lists galactic positions and possible source identifications in order to provide the astronomical community with a list of time-variable objects that can now be repeatedly observed at other wavelengths. We expect the total number of time-variable source detections to increase as the GALEX mission progresses, such that later version numbers of the GUVV catalog will contain substantially more variable sources.

We present 741 new photometric observations for 22 Cepheids with periods between 3 and 8 days. Many of the stars are probable type II Cepheids, but we have included some type I Cepheids for comparison. The shapes and stability of the shapes of the light curves, the stability of the periods, and the scatter of individual data points are discussed. Although none of these proves to be a reliable discriminator between type I and type II Cepheids, they do permit the identification of several unusual stars.

We report the angular diameters of two Mira variables (U Ari and Z Sco), three semiregular (SR) and irregular variables (SW Vir, η Gem, and μ Gem), and a supergiant SR variable (TV Gem) by lunar occultation observations in the near-IR broad K band (2.2 μm). Lunar occultations of η Gem and μ Gem were also observed for the first time simultaneously in both the K and L' bands, yielding angular diameters at 2.2 and 3.8 μm. Effective temperatures and linear radii are also derived for all the observed sources and compared with earlier measurements. The mode of pulsation of both Mira and SR sources in our sample is discussed.

We present new high-dispersion, long-slit, infrared (IR) spectra of the double-shell bipolar planetary nebula M2-9 in the emission lines [Fe II] λ16435 and H₂v = 1–0 S(1) λ21218. H₂ spectra reveal for the first time the kinematic structure of the outer shell in M2-9. Kinematics of the inner shell, traced by [Fe II], resemble those of optical forbidden lines like [N II] λ6583, although we note subtle differences. [Fe II] and H₂ shells have expansion speeds roughly proportional to distance from the star ("Hubble" flows) and share the same dynamical age of 1200–2000 yr, depending on the distance to M2-9. Thus, the inner ionized lobes and outer molecular lobes, as well as the molecular torus and "outer loops" measured by other observers, were all formed around the same time. Consequently, their nested structure likely arises from an excitation gradient rather than independent ejections. H₂ and [Fe II] emission is distributed more uniformly than [N II], and IR lines are not dominated by the moving ionization pattern like visual-wavelength lines. We suggest that this is because IR lines of [Fe II] and H₂ are excited by relatively isotropic far-UV radiation (Balmer continuum), whereas optical lines respond to a directed rotating beam of Lyman continuum. Finally, we highlight intriguing similarities between M2-9 and the Homunculus of η Car, despite the different central engines powering the two nebulae.