Table of contents

We compare molecular gas traced by ¹²CO (2–1) maps from the HERACLES survey, with tracers of the recent star formation rate (SFR) across 30 nearby disk galaxies. We demonstrate a first-order linear correspondence between Σ_mol and Σ_SFR but also find important second-order systematic variations in the apparent molecular gas depletion time, $\tau _{\rm dep}^{\rm mol} = \Sigma _{\rm mol} / \Sigma _{\rm SFR}$. At the 1 kpc common resolution of HERACLES, CO emission correlates closely with many tracers of the recent SFR. Weighting each line of sight equally, using a fixed α_CO equivalent to the Milky Way value, our data yield a molecular gas depletion time, $\tau _{\rm dep}^{\rm mol}=\Sigma _{\rm mol}/\Sigma _{\rm SFR} \approx 2.2$ Gyr with 0.3 dex 1σ scatter, in very good agreement with recent literature data. We apply a forward-modeling approach to constrain the power-law index, N, that relates the SFR surface density and the molecular gas surface density, $\Sigma _{\rm SFR} \propto \Sigma _{\rm mol}^N$. We find N = 1 ± 0.15 for our full data set with some scatter from galaxy to galaxy. This also agrees with recent work, but we caution that a power-law treatment oversimplifies the topic given that we observe correlations between $\tau _{\rm dep}^{\rm mol}$ and other local and global quantities. The strongest of these are a decreased $\tau _{\rm dep}^{\rm mol}$ in low-mass, low-metallicity galaxies and a correlation of the kpc-scale $\tau _{\rm dep}^{\rm mol}$ with dust-to-gas ratio, D/G. These correlations can be explained by a CO-to-H₂ conversion factor (α_CO) that depends on dust shielding, and thus D/G, in the theoretically expected way. This is not a unique interpretation, but external evidence of conversion factor variations makes this the most conservative explanation of the strongest observed $\tau _{\rm dep}^{\rm mol}$ trends. After applying a D/G-dependent α_CO, some weak correlations between $\tau _{\rm dep}^{\rm mol}$ and local conditions persist. In particular, we observe lower $\tau _{\rm dep}^{\rm mol}$ and enhanced CO excitation associated with nuclear gas concentrations in a subset of our targets. These appear to reflect real enhancements in the rate of star formation per unit gas, and although the distribution of τ_dep does not appear bimodal in galaxy centers, τ_dep does appear multivalued at fixed Σ_H2, supporting the idea of "disk" and "starburst" modes driven by other environmental parameters.

In this paper, we present surface brightness profiles for 79 globular clusters in M31, using images observed with the Hubble Space Telescope, some of which are from new observations. The structural and dynamical parameters are derived from fitting the profiles to several different models for the first time. The results show that in the majority of cases, King models fit the M31 clusters just as well as Wilson models and better than Sérsic models. However, there are 11 clusters best fitted by Sérsic models with the Sérsic index n > 2, meaning that they have cuspy central density profiles. These clusters may be the well-known core-collapsed candidates. There is a bimodality in the size distribution of M31 clusters at large radii, which is different from their Galactic counterparts. In general, the properties of clusters in M31 and the Milky Way fall in the same regions of parameter spaces. The tight correlations of cluster properties indicate a "fundamental plane" for clusters, which reflects some universal physical conditions and processes operating at the epoch of cluster formation.

We present a sample of ∼5000 RR Lyrae stars selected from the recalibrated LINEAR data set and detected at heliocentric distances between 5 kpc and 30 kpc over ∼8000 deg² of sky. The coordinates and light curve properties, such as period and Oosterhoff type, are made publicly available. We analyze in detail the light curve properties and Galactic distribution of the subset of ∼4000 type ab RR Lyrae (RRab) stars, including a search for new halo substructures and the number density distribution as a function of Oosterhoff type. We find evidence for the Oosterhoff dichotomy among field RR Lyrae stars, with the ratio of the type II and I subsamples of about 1:4, but with a weaker separation than for globular cluster stars. The wide sky coverage and depth of this sample allow unique constraints for the number density distribution of halo RRab stars as a function of galactocentric distance: it can be described as an oblate ellipsoid with an axis ratio q = 0.63 and with either a single or a double power law with a power-law index in the range −2 to −3. Consistent with previous studies, we find that the Oosterhoff type II subsample has a steeper number density profile than the Oosterhoff type I subsample. Using the group-finding algorithm EnLink, we detected seven candidate halo groups, only one of which is statistically spurious. Three of these groups are near globular clusters (M53/NGC 5053, M3, M13), and one is near a known halo substructure (Virgo Stellar Stream); the remaining three groups do not seem to be near any known halo substructures or globular clusters and seem to have a higher ratio of Oosterhoff type II to Oosterhoff type I RRab stars than what is found in the halo. The extended morphology and the position (outside the tidal radius) of some of the groups near globular clusters are suggestive of tidal streams possibly originating from globular clusters. Spectroscopic follow-up of detected halo groups is encouraged.

We apply one of the lazy learning methods, the k-nearest neighbor (kNN) algorithm, to estimate the photometric redshifts of quasars based on various data sets from the Sloan Digital Sky Survey (SDSS), the UKIRT Infrared Deep Sky Survey (UKIDSS), and the Wide-field Infrared Survey Explorer (WISE; the SDSS sample, the SDSS–UKIDSS sample, the SDSS–WISE sample, and the SDSS–UKIDSS–WISE sample). The influence of the k value and different input patterns on the performance of kNN is discussed. kNN performs best when k is different with a special input pattern for a special data set. The best result belongs to the SDSS–UKIDSS–WISE sample. The experimental results generally show that the more information from more bands, the better performance of photometric redshift estimation with kNN. The results also demonstrate that kNN using multiband data can effectively solve the catastrophic failure of photometric redshift estimation, which is met by many machine learning methods. Compared with the performance of various other methods of estimating the photometric redshifts of quasars, kNN based on KD-Tree shows superiority, exhibiting the best accuracy.

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He i λ10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities ∼400 km s⁻¹ appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.

I have discovered a prominent light echo around the low-luminosity Type II-plateau supernova (SN) 2008bk in NGC 7793, seen in archival images obtained with the Wide Field Channel of the Advanced Camera for Surveys on board the Hubble Space Telescope (HST). The echo is a partial ring, brighter to the north and east than to the south and west. The analysis of the echo I present suggests that it is due to the SN light pulse scattered by a sheet, or sheets, of dust located ≈15 pc from the SN. The composition of the dust is assumed to be of standard Galactic diffuse interstellar grains. The visual extinction of the dust responsible for the echo is A_V ≈ 0.05 mag in addition to the extinction due to the Galactic foreground toward the host galaxy. That the SN experienced much less overall extinction implies that it is seen through a less dense portion of the interstellar medium in its environment. The late-time HST photometry of SN 2008bk also clearly demonstrates that the progenitor star has vanished.

We examine the gravitational capture probability of colliding particles in circumplanetary particle disks and accretion rates of small particles onto an embedded moonlet, using analytic calculation, three-body orbital integrations, and N-body simulations. Expanding our previous work, we take into account the Rayleigh distribution of particles' orbital eccentricities and inclinations in our analytic calculation and orbital integration and confirm agreement between them when the particle velocity dispersion is comparable to or larger than their mutual escape velocity and the ratio of the sum of the physical radii of colliding particles to their mutual Hill radius ($\tilde{r}_\mathrm{p}$) is much smaller than unity. As shown by our previous work, the capture probability decreases significantly when the velocity dispersion is larger than the escape velocity and/or $\tilde{r}_\mathrm{p} \gtrsim 0.7$. Rough surfaces of particles can enhance the capture probability. We compare the results of three-body calculations with N-body simulations for accretion of small particles by an embedded moonlet and find agreement at the initial stage of accretion. However, when particles forming an aggregate on the moonlet surface nearly fill the Hill sphere, the aggregate reaches a quasi-steady state with a nearly constant number of particles covering the moonlet, and the accretion rate is significantly reduced compared to the three-body results.

Near-Earth asteroid (162173) 1999 JU₃ (henceforth JU₃) is a potentially hazardous asteroid and the target of the Japanese Aerospace Exploration Agency's Hayabusa-2 sample return mission. JU₃ is also a backup target for two other sample return missions: NASA's OSIRIS-REx and the European Space Agency's Marco Polo-R. We use dynamical information to identify an inner-belt, low-inclination origin through the ν₆ resonance, more specifically, the region with 2.15 AU < a < 2.5 AU and i < 8°. The geometric albedo of JU₃ is 0.07 ± 0.01, and this inner-belt region contains four well-defined low-albedo asteroid families (Clarissa, Erigone, Polana, and Sulamitis), plus a recently identified background population of low-albedo asteroids outside these families. Only two of these five groups, the background and the Polana family, deliver JU₃-sized asteroids to the ν₆ resonance, and the background delivers significantly more JU₃-sized asteroids. The available spectral evidence is also diagnostic; the visible and near-infrared spectra of JU₃ indicate it is a C-type asteroid, which is compatible with members of the background, but not with the Polana family because it contains primarily B-type asteroids. Hence, this background population of low-albedo asteroids is the most likely source of JU₃.

For the restricted three-body problem, we propose an accurate orbital integration scheme that retains all conserved quantities of the two-body problem with two primaries and approximately preserves the Jacobi integral. The scheme is obtained by taking the limit as mass approaches zero in the discrete-time general three-body problem. For a long time interval, the proposed scheme precisely reproduces various periodic orbits that cannot be accurately computed by other generic integrators.

V401 Cyg is a quadruple system in which the spectroscopic signature of a close-in tertiary and a distant visual companion star were reported. Orbital properties of the close-in companion should provide valuable information on the formation of close binaries and stellar dynamical interaction. By analyzing new times of minimum light together with those collected from the literature, we discovered that the observed−calculated (O − C) curve of V401 Cyg shows a cyclic change with a short period of 3.5 yr and a semi-amplitude of 0.00436 days while it undergoes an upward parabolic variation. Those photoelectric and CCD data covered more than two cycles and were analyzed for the light-travel time effect via the presence of the tertiary companion. The mass of the third body was determined to be M₃sin i' = 0.65(± 0.08) M_☉, which is close to the value estimated from the spectroscopic data (M₃ ∼ 0.64 M_☉). This reveals that the orbital inclination of the tertiary was about i' ∼ 90°, indicating that the contact components of V401 Cyg have the possibility of being eclipsed by the tertiary at an orbital distance of about 3.0 AU, and it may be a triply eclipsing hierarchical triple system. The upward parabolic change indicates a period increase at a rate of $\dot{P}=1.5\times {10^{-7}}$ revealing a mass transfer from the secondary to the primary ($\dot{M}_{2}=5.9\times {10^{-8}}$M_☉ yr⁻¹). This is consistent with the predictions of the theory of thermal relaxation oscillation (TRO) suggesting that V401 Cyg is undergoing an expanding-orbit stage in the TRO cycles.

Fundamental spectroscopic determination of projected rotation rates of slowly rotating stars is challenging because the rotational broadening of the spectral lines is often comparable to, or smaller than, the broadening from other sources, most notably macroturbulence. Fourier techniques have the advantage over direct profile matching when the observed profiles are complete, but when the profiles are severely blended, the Fourier analysis is compromised. A process of modeling partial profiles for determining the rotation rate for stars having blended spectral lines is investigated and applied to the evolved star α Hya (K3 II–III). Projected rotation higher than 5 km s⁻¹ can be definitively ruled out for this star. Not all lines are equally good, depending on the amount of blending and also depending on the strength of the line, as the balance between the thermal and non-thermal components changes. A modest ambiguity arises between macroturbulence and rotational broadening, but a careful look at the differences between the observations and the models allows one to measure the rotation with acceptable precision. The result for α Hya is v sin i = 2.6 ± 0.3 km s⁻¹.

Integral field spectroscopy of 11 Type Ib/Ic supernova (SN Ib/Ic) explosion sites in nearby galaxies has been obtained using UH88/SNIFS and Gemini-N/GMOS. The use of integral field spectroscopy enables us to obtain both spatial and spectral information about the explosion site, enabling the identification of the parent stellar population of the SN progenitor star. The spectrum of the parent population provides metallicity determination via strong-line method and age estimation obtained via comparison with simple stellar population models. We adopt this information as the metallicity and age of the SN progenitor, under the assumption that it was coeval with the parent stellar population. The age of the star corresponds to its lifetime, which in turn gives the estimate of its initial mass. With this method we were able to determine both the metallicity and initial (zero-age main sequence) mass of the progenitor stars of SNe Ib and Ic. We found that on average SN Ic explosion sites are more metal-rich and younger than SN Ib sites. The initial mass of the progenitors derived from parent stellar population age suggests that SN Ic has more massive progenitors than SN Ib. In addition, we also found indication that some of our SN progenitors are less massive than ∼25 M_☉, indicating that they may have been stars in a close binary system that have lost their outer envelope via binary interactions to produce SNe Ib/Ic, instead of single Wolf–Rayet stars. These findings support the current suggestions that both binary and single progenitor channels are in effect in producing SNe Ib/Ic. This work also demonstrates the power of integral field spectroscopy in investigating SN environments and active star-forming regions.

Thirteen explosion sites of Type II-P and II-L supernovae (SNe) in nearby galaxies have been observed using integral field spectroscopy, enabling both spatial and spectral study of the explosion sites. We used the properties of the parent stellar population of the coeval SN progenitor star to derive its metallicity and initial mass. The spectrum of the parent stellar population yields estimates of metallicity via the strong-line method and age via a comparison with simple stellar population models. These metallicity and age parameters are adopted for the progenitor star. Age, or lifetime of the star, was used to derive the initial (zero-age main sequence) mass of the star using comparisons with stellar evolution models. With this technique, we were able to determine the metallicities and initial masses of the SN progenitors in our sample. Our results indicate that some Type II SN progenitors may have been stars with masses comparable to those of SN Ib/c progenitors.

We present the design and performance of the multi-object fiber spectrographs for the Sloan Digital Sky Survey (SDSS) and their upgrade for the Baryon Oscillation Spectroscopic Survey (BOSS). Originally commissioned in Fall 1999 on the 2.5 m aperture Sloan Telescope at Apache Point Observatory, the spectrographs produced more than 1.5 million spectra for the SDSS and SDSS-II surveys, enabling a wide variety of Galactic and extra-galactic science including the first observation of baryon acoustic oscillations in 2005. The spectrographs were upgraded in 2009 and are currently in use for BOSS, the flagship survey of the third-generation SDSS-III project. BOSS will measure redshifts of 1.35 million massive galaxies to redshift 0.7 and Lyα absorption of 160,000 high redshift quasars over 10,000 deg² of sky, making percent level measurements of the absolute cosmic distance scale of the universe and placing tight constraints on the equation of state of dark energy. The twin multi-object fiber spectrographs utilize a simple optical layout with reflective collimators, gratings, all-refractive cameras, and state-of-the-art CCD detectors to produce hundreds of spectra simultaneously in two channels over a bandpass covering the near-ultraviolet to the near-infrared, with a resolving power R = λ/FWHM ∼ 2000. Building on proven heritage, the spectrographs were upgraded for BOSS with volume-phase holographic gratings and modern CCD detectors, improving the peak throughput by nearly a factor of two, extending the bandpass to cover 360 nm < λ < 1000 nm, and increasing the number of fibers from 640 to 1000 per exposure. In this paper we describe the original SDSS spectrograph design and the upgrades implemented for BOSS, and document the predicted and measured performances.

We have measured the absolute proper motions of globular clusters NGC 6397, NGC 6626 (M22), and NGC 6656 (M28) as part of our ongoing Southern Proper-Motion Program. The reference system is the ICRS via Hipparcos stars for these three low-Galactic-latitude clusters. Formal errors range between ∼0.3 and 0.7 mas yr⁻¹. Notable is the result for NGC 6397, which differs by 2.5 mas yr⁻¹ from two Hubble Space Telescope determinations while agreeing with previous ground-based ones. We determine orbits for all three clusters in an axisymmetric and barred model of the Galaxy and discuss these in the context of globular-cluster formation. M22 is a well-known cluster with an iron abundance spread; such clusters are now believed to have formed in massive parent systems that can retain ejecta of core-collapsed supernovae. We find that the five currently accepted globular clusters with iron/calcium abundance spread show orbits unrelated to each other, thus suggesting at least five independent, massive progenitors that have contributed to the build-up of the Milky-Way halo.

A total of ∼640, 000 objects from the LAMOST pilot survey have been publicly released. In this work, we present a catalog of DA white dwarfs (DAWDs) from the entire pilot survey. We outline a new algorithm for the selection of white dwarfs (WDs) by fitting Sérsic profiles to the Balmer Hβ, Hγ, and Hδ lines of the spectra, and calculating the equivalent width of the Ca ii K line. Two thousand nine hundred sixty-four candidates are selected by constraining the fitting parameters and the equivalent width of the Ca ii K line. All the spectra of candidates are visually inspected. We identify 230 DAWDs (59 of which are already included in the Villanova and SDSS WD catalogs), 20 of which are DAWDs with non-degenerate companions. In addition, 128 candidates are classified as DAWDs/subdwarfs, which means the classifications are ambiguous. The result is consistent with the expected DAWD number estimated based on the LEGUE target selection algorithm.

New multi-color photometry for the eclipsing binary DZ Psc was performed in 2011 and 2012 using the 85 cm telescope at the Xinglong Station of the National Astronomical Observatories of China. Using the updated Wilson–Devinney (W–D) code, we deduced two sets of photometric solutions. The overcontact degree is f = 89.7(± 1.0)%, identifying DZ Psc as a deep, low mass ratio overcontact binary. The asymmetric light curves (i.e., LC₂ in 2012) were modeled by a hot spot on the primary star. Based on all of the available light minimum times, we discovered that the orbital period of DZ Psc may be undergoing a secular period increase with a cyclic variation. The modulated period and semi-amplitude of this oscillation are P_mod = 11.89(± 0.19) yr and A = 0.0064(± 0.0006) days, which may be possibly attributed to either cyclic magnetic activity or light–time effect due to the third body. The long-term period increases at a rate of $dP/dt=+7.43(\pm 0.17)\times 10^{-7}\mathrm{\,{\rm days}\, yr^{-1}}$, which may be interpreted as conserved mass transfer from the less massive component to the more massive one. With mass transferring, DZ Psc will finally merge into a rapid-rotation single star when J_spin/J_orb > 1/3.

The Kuiper Belt is a remnant from the early solar system and its size distribution contains many important constraints that can be used to test models of planet formation and collisional evolution. We show, by comparing observations with theoretical models, that the observed Kuiper Belt size distribution is well matched by coagulation models, which start with an initial planetesimal population with radii of about 1 km, and subsequent collisional evolution. We find that the observed size distribution above R ∼ 30 km is primordial, i.e., it has not been modified by collisional evolution over the age of the solar system, and that the size distribution below R ∼ 30 km has been modified by collisions and that its slope is well matched by collisional evolution models that use published strength laws. We investigate in detail the resulting size distribution of bodies ranging from 0.01 km to 30 km and find that its slope changes several times as a function of radius before approaching the expected value for an equilibrium collisional cascade of material strength dominated bodies for R ≲ 0.1 km. Compared to a single power-law size distribution that would span the whole range from 0.01 km to 30 km, we find in general a strong deficit of bodies around R ∼ 10 km and a strong excess of bodies around 2 km in radius. This deficit and excess of bodies are caused by the planetesimal size distribution left over from the runaway growth phase, which left most of the initial mass in small planetesimals while only a small fraction of the total mass is converted into large protoplanets. This excess mass in small planetesimals leaves a permanent signature in the size distribution of small bodies that is not erased after 4.5 Gyr of collisional evolution. Observations of the small Kuiper Belt Object (KBO) size distribution can therefore test if large KBOs grew as a result of runaway growth and constrained the initial planetesimal sizes. We find that results from recent KBO occultation surveys and the observed KBO size distribution can be best matched by an initial planetesimal population that contained about equal mass per logarithmic mass bin in bodies ranging from 0.4 km to 4 km in radius. We further find that we cannot match the observed KBO size distribution if most of the planetesimal mass was contained in bodies that were 10 km in radius or larger simply because their resulting size distribution cannot be sufficiently depleted over 4.5 Gyr to match observations.

We present phase-resolved near-infrared photometry and spectroscopy of the classical nova (CN) V1500 Cyg to explore whether cyclotron emission is present in this system. While the spectroscopy do not indicate the presence of discrete cyclotron harmonic emission, the light curves suggest that a sizable fraction of its near-infrared fluxes are due to this component. The light curves of V1500 Cyg appear to remain dominated by emission from the heated face of the secondary star in this system. We have used infrared spectroscopy and photometry to search for other potential magnetic systems among old CNe. We have found that the infrared light curves of V1974 Cyg superficially resemble those of V1500 Cyg, suggesting a highly irradiated companion. The old novae V446 Her and QV Vul have light curves with large amplitude variations like those seen in polars, suggesting they might have magnetic primaries. We extract photometry for 79 old novae from the Two Micron All Sky Survey Point Source Catalog and use those data to derive the mean, un-reddened infrared colors of quiescent novae. We also extract WISE data for these objects and find that 45 of them were detected. Surprisingly, a number of these systems were detected in the WISE 22 μm band. While two of those objects produced significant dust shells (V705 Cas and V445 Pup), the others did not. It appears that line emission from their ionized ejected shells is the most likely explanation for those detections.

By analyzing multi-color light curves of the newly discovered W UMa-type binary, MR Com, we discovered that it is a shallow-contact binary with a degree of contact factor of f = 10.0% ± 2.1%. Photometric solutions reveal that MR Com is a W-type system with a mass ratio of q = 3.9 where the less massive component is about 90 K hotter than the more massive one. By investigating all of the available times of minimum light, we found that the general trend of the Observed−Calculated (O − C) curve shows a downward parabolic variation while it undergoes a cyclic variation with a small amplitude of 0.0031 days and a period of 10.1 yr. The downward parabolic change corresponds to a long-term decrease in the orbital period at a rate of $\dot{P}=-5.3\times {10^{-7}}$ days yr⁻¹ that may be caused by a combination of a mass transfer and an angular momentum loss (AML) via magnetic braking. Among the 16 shallow-contact systems with a decreasing orbital period, MR Com has the lowest mass ratio (e.g., 1/q = 0.26). The shallow-contact configuration, the low-mass ratio, and the long-term period decrease all suggest that systems similar to MR Com are on the AML-controlled stage of the evolutionary scheme proposed by Qian. They will oscillate around a critical mass ratio and evolve into a deep contact with a higher mass ratio. The small-amplitude cyclic change in the O − C curve was analyzed for the light-travel time effect via the presence of an extremely cool stellar companion.

Open clusters are very useful examples to explain the constraint of the nucleosynthesis process with the luminosities of stars because the distances of the clusters are better known than those of field stars. We carried out a detailed spectroscopic analysis to derive the chemical composition of two red giants in the young open cluster NGC 5822, NGC 5822-2, and NGC 5822-201. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code moog. The abundances of the light elements were derived using the spectral synthesis technique. We found that NGC 5822-2 and -201 have, respectively, a mean overabundance of the elements created by the s-process, "s," with the notation [s/Fe] of 0.77 ± 0.12 and 0.83 ± 0.05. These values are higher than those for field giants of similar metallicity. We also found that NGC 5822-2 and -201 have, respectively, luminosities of 140 L_☉ and 76 L_☉, which are much lower than the luminosity of an asymptotic giant branch star. We conclude that NGC 5822-2 and NGC 5822-201 are two new barium stars first identified in the open cluster NGC 5822. The mass transfer hypothesis is the best scenario to explain the observed overabundances.

We analyze extensive BVR_CI_C photometry and radial velocity measurements for three double-lined deeply eclipsing binary stars in the field of the old open cluster NGC 7142. The short period (P = 1.9096825 days) detached binary V375 Cep is a high probability cluster member, and has a total eclipse of the secondary star. The characteristics of the primary star (M = 1.288 ± 0.017 M_☉) at the cluster turnoff indicate an age of 3.6 Gyr (with a random uncertainty of 0.25 Gyr), consistent with earlier analysis of the color–magnitude diagram. The secondary star (M = 0.871 ± 0.008 M_☉) is not expected to have evolved significantly, but its radius is more than 10% larger than predicted by models. Because this binary system has a known age, it is useful for testing the idea that radius inflation can occur in short period binaries for stars with significant convective envelopes due to the inhibition of energy transport by magnetic fields. The brighter star in the binary also produces a precision estimate of the distance modulus, independent of reddening estimates: (m − M)_V = 12.86 ± 0.07. The other two eclipsing binary systems are not cluster members, although one of the systems (V2) could only be conclusively ruled out as a present or former member once the stellar characteristics were determined. That binary is within 05 of edge-on, is in a fairly long-period eccentric binary, and contains two almost indistinguishable stars. The other binary (V1) has a small but nonzero eccentricity (e = 0.038) in spite of having an orbital period under 5 days.

The luminosities, colors, and Hα emission for 429 H ii regions in 54 low surface brightness (LSB) galaxies are presented. While the number of H ii regions per galaxy is lower in LSB galaxies compared to star-forming irregulars and spirals, there is no indication that the size or luminosity function of H ii regions differs from other galaxy types. The lower number of H ii regions per galaxy is consistent with their lower total star formation rates. The fraction of the total L_Hα contributed by H ii regions varies from 10% to 90% in LSB galaxies (the rest of the Hα emission being associated with a diffuse component) with no correlation with galaxy stellar or gas mass. Bright H ii regions have bluer colors, similar to the trend in spirals; their number and luminosities are consistent with the hypothesis that they are produced by the same H ii luminosity function as spirals. Comparison with stellar population models indicates that the brightest H ii regions in LSB galaxies range in cluster mass from a few 10³ M_☉ (e.g., ρ Oph) to globular-cluster-sized systems (e.g., 30 Dor) and that their ages are consistent with clusters from 2 to 15 Myr old. The faintest H ii regions are comparable to those in the LMC powered by a single O or B star. Thus, star formation in LSB galaxies covers the full range of stellar cluster mass.

We analyze high angular and velocity resolution H i line data of two LITTLE THINGS blue compact dwarfs (BCDs): Haro 29 and Haro 36. Both of these BCDs are disturbed morphologically and kinematically. Haro 29's H i data reveal a kinematic major axis that is offset from the optical major axis, and a disturbed outer H i component, indicating that Haro 29 may have had a past interaction. Position–velocity diagrams of Haro 36 indicate that it has two kinematically separate components at its center and a likely tidal tail in front of the galaxy. We find that Haro 36 most likely had an interaction in the past, is currently interacting with an unknown companion, or is a merger remnant.

We present proper motions and astrometric membership analysis for 15,750 stars around the intermediate-age open cluster NGC 6819. The accuracy of relative proper motions for well-measured stars ranges from ∼0.2 mas yr⁻¹ within 10' of the cluster center to 1.1 mas yr⁻¹ outside this radius. In the proper motion vector-point diagram, the separation between the cluster members and field stars is convincing down to V ∼ 18 and within 10' from the cluster center. The formal sum of membership probabilities indicates a total of ∼2500 cluster members down to V ∼ 22. We confirm the cluster membership of several variable stars, including some eclipsing binaries. The estimated absolute proper motion of NGC 6819 is $\mu _x^{\rm abs}=-2.6\pm 0.5$ and $\mu _y^{\rm abs}=-4.2\pm 0.5$ mas yr⁻¹. A cross-identification between the proper motion catalog and a list of X-ray sources in the field of NGC 6819 resulted in a number of new likely optical counterparts, including a candidate CV. For the first time we show that there is significant differential reddening toward NGC 6819.