Table of contents

We present a catalog of over 130,000 quasar candidates with near-infrared (NIR) photometric properties, with an areal coverage of approximately 1200 deg². This is achieved by matching the Sloan Digital Sky Survey (SDSS) in the optical ugriz bands to the UKIRT Infrared Digital Sky Survey (UKIDSS) Large Area Survey (LAS) in the NIR YJHK bands. We match the ≈1 million SDSS DR6 Photometric Quasar catalog to Data Release 3 of the UKIDSS LAS (ULAS) and produce a catalog with 130,827 objects with detections in one or more NIR bands, of which 74,351 objects have optical and K-band detections and 42,133 objects have the full nine-band photometry. The majority (∼85%) of the SDSS objects were not matched simply because these were not covered by the ULAS. The positional standard deviation of the SDSS Quasar to ULAS matches is δ_R.A. = 01370 and δ_decl. = 01314. We find an absolute systematic astrometric offset between the SDSS Quasar catalog and the UKIDSS LAS, of |R.A._offset| = 0025 and |decl._offset| = 0040; we suggest the nature of this offset to be due to the matching of catalog, rather than image, level data. Our matched catalog has a surface density of ≈53 deg⁻² for K ⩽ 18.27 objects; tests using our matched catalog, along with data from the UKIDSS Deep Extragalactic Survey, imply that our limiting magnitude is i ≈ 20.6. Color–redshift diagrams, for the optical and NIR, show a close agreement between our matched catalog and recent quasar color models at redshift z ≲ 2.0, while at higher redshifts, the models generally appear to be bluer than the mean observed quasar colors. The gJK and giK color spaces are used to examine methods of differentiating between stars and (mid-redshift) quasars, the key to currently ongoing quasar surveys. Finally, we report on the NIR photometric properties of high, z > 4.6, and very high, z > 5.7, redshift previously discovered quasars.

Recent observations of UGC 4879 with the Advanced Camera for Surveys on the Hubble Space Telescope confirm that it is a nearby isolated dwarf irregular galaxy. We measure a distance of 1.36 ± 0.03 Mpc using the tip of the red giant branch method. This distance puts UGC 4879 beyond the radius of first turnaround of the Local Group and ∼700 kpc from its nearest neighbor Leo A. This isolation makes this galaxy an ideal laboratory for studying pristine star formation uncomplicated by interactions with other galaxies. We present the star formation history of UGC 4879 derived from simulated color–magnitude diagrams.

We present the chromospheric activity (CA) levels, metallicities, and full space motions for 41 F, G, K, and M dwarf stars in 36 wide binary systems. Thirty-one of the binaries contain a white dwarf (WD) component. In such binaries, the total age can be estimated by adding the cooling age of the WD to an estimate of the progenitor's main-sequence lifetime. To better understand how CA correlates to stellar age, 14 cluster member stars were also observed. Our observations demonstrate for the first time that, in general, CA decays with age from 50 Myr to at least 8 Gyr for stars with 1.0 ⩽ V − I ⩽ 2.4. However, little change occurs in the CA level for stars with V − I < 1.0 between 1 Gyr and 5 Gyr, consistent with the results of Pace et al. Our sample also exhibits a negative correlation between the stellar age and metallicity, a positive correlation between the stellar age and W space velocity component, and the W velocity dispersion increases with age. Finally, the population membership of these wide binaries is examined based upon their U, V, W kinematics, metallicity, and CA. We conclude that wide binaries are similar to field and cluster stars in these respects. More importantly, they span a much more continuous range in age and metallicity than is afforded by nearby clusters.

We present a variability analysis of the early-release first quarter of data publicly released by the Kepler project. Using the stellar parameters from the Kepler Input Catalog, we have separated the sample into 129,000 dwarfs and 17,000 giants and further sub-divided the luminosity classes into temperature bins corresponding approximately to the spectral classes A, F, G, K, and M. Utilizing the inherent sampling and time baseline of the public data set (30 minute sampling and 33.5 day baseline), we have explored the variability of the stellar sample. The overall variability rate of the dwarfs is 25% for the entire sample, but can reach 100% for the brightest groups of stars in the sample. G dwarfs are found to be the most stable with a dispersion floor of σ ∼ 0.04 mmag. At the precision of Kepler, >95% of the giant stars are variable with a noise floor of ∼0.1 mmag, 0.3 mmag, and 10 mmag for the G giants, K giants, and M giants, respectively. The photometric dispersion of the giants is consistent with acoustic variations of the photosphere; the photometrically derived predicted radial velocity distribution for the K giants is in agreement with the measured radial velocity distribution. We have also briefly explored the variability fraction as a function of data set baseline (1–33 days), at the native 30 minute sampling of the public Kepler data. To within the limitations of the data, we find that the overall variability fractions increase as the data set baseline is increased from 1 day to 33 days, in particular for the most variable stars. The lower mass M dwarf, K dwarf, and G dwarf stars increase their variability more significantly than the higher mass F dwarf and A dwarf stars as the time baseline is increased, indicating that the variability of the lower mass stars is mostly characterized by timescales of weeks while the variability of the higher mass stars is mostly characterized by timescales of days. A study of the distribution of the variability as a function of galactic latitude suggests that sources closer to the galactic plane are more variable. This may be the result of sampling differing populations (i.e., ages) as a function of latitude or may be the result of higher background contamination that is inflating the variability fractions at lower latitudes. A comparison of the M dwarf statistics to the variability of 29 known bright M dwarfs indicates that the M dwarfs are primarily variable on timescales of weeks or longer presumably dominated by spots and binarity. On shorter timescales of hours, which are relevant for planetary transit detection, the stars are significantly less variable, with ∼80% having 12 hr dispersions of 0.5 mmag or less.

Space missions to near-Earth objects (NEOs) are being planned at all major space agencies, and recently a manned mission to an NEO was announced as a NASA goal. Efforts to find and select suitable targets (plus backup targets) are severely hampered by our lack of knowledge of the physical properties of dynamically favorable NEOs. In particular, current mission scenarios tend to favor primitive low-albedo objects. For the vast majority of NEOs, the albedo is unknown. Here we report new constraints on the size and albedo of 65 NEOs with rendezvous Δv <7 km s⁻¹. Our results are based on thermal-IR flux data obtained in the framework of our ongoing (2009–2011) ExploreNEOs survey using NASA's "Warm-Spitzer" space telescope. As of 2010 July 14, we have results for 293 objects in hand (including the 65 low-Δv NEOs presented here); before the end of 2011, we expect to have measured the size and albedo of ∼700 NEOs (including probably ∼160 low-Δv NEOs). While there are reasons to believe that primitive volatile-rich materials are universally low in albedo, the converse need not be true: the orbital evolution of some dark objects likely has caused them to lose their volatiles by coming too close to the Sun. For all our targets, we give the closest perihelion distance they are likely to have reached (using orbital integrations from Marchi et al. 2009) and corresponding upper limits on the past surface temperature. Low-Δv objects for which both albedo and thermal history may suggest a primitive composition include (162998) 2001 SK162, (68372) 2001 PM9, and (100085) 1992 UY4.

We have identified a complete, flux-limited (S₁₆₀>120 mJy) sample of 160 μm selected sources from Spitzer observations of the 1 deg²Infrared Space Observatory (ISO) Deep Field region in the Lockman Hole (LH). Ground-based UV, optical, and near-infrared (NIR) photometry and optical spectroscopy have been used to determine colors, redshifts, and masses for the complete sample of 40 galaxies. Spitzer-IRAC+MIPS photometry, supplemented by ISOPHOT data at 90 μm and 170 μm, has been used to calculate accurate total infrared luminosities, L_IR(8–1000 μm), and to determine the IR luminosity function (LF) of luminous infrared galaxies (LIRGs). The maximum observed redshift is z ∼ 0.80 and the maximum total infrared luminosity is log (L_IR/L_☉) = 12.74. Over the luminosity range log (L_IR/L_☉) = 10–12, the LF for LIRGs in the LH Deep Field is similar to that found previously for local sources at similar infrared luminosities. The mean host galaxy mass, log (M/M_☉) = 10.7, and dominance of H ii-region spectral types, is also similar to what has been found for local LIRGs, suggesting that intense starbursts likely power the bulk of the infrared luminosity for sources in this range of L_IR. However for the most luminous sources, log (L_IR/L_☉)>12.0, we find evidence for strong evolution in the LF ∝(1 + z)^6±1, assuming pure number density evolution. These ultraluminous infrared galaxies (ULIRGs) have a larger mean host mass, log (M/M_☉) = 11.0, and exhibit disturbed morphologies consistent with strong interactions/mergers, and they are also more likely to be characterized by starburst–active galactic nucleus (AGN) composite or AGN spectral types.

By tracing the distribution of cool dust in the extended envelopes of post-asymptotic giant branch stars and (proto)-planetary nebulae ((P)PNe), we aim to recover, or constrain, the mass-loss history experienced by these stars in their recent past. The Far-Infrared Surveyor (FIS) instrument on board the AKARI satellite was used to obtain far-infrared maps for a selected sample of post-AGB stars and (P)PNe. We derived flux densities (aperture photometry) for 13 post-AGB stars and (P)PNe at four far-infrared wavelengths (65, 90, 140, and 160 μm). Radial (azimuthally averaged) profiles are used to investigate the presence of extended emission from cool dust. No (detached) extended emission is detected for any target in our sample at levels significant with respect to background and cirrus emission. Only IRAS 21046+4739 reveals tentative excess emission between 30'' and 130''. Estimates of the total dust and gas mass from the obtained maps indicate that the envelope masses of these stars should be large in order to be detected with the AKARI FIS. Imaging with higher sensitivity and higher spatial resolution is needed to detect and resolve, if present, any cool compact or extended emission associated with these evolved stars.

This paper presents the only space-borne optical-imaging observations of the 2004 June 8 transit of Venus, the first such transit visible from Earth since AD 1882. The high-resolution, high-cadence satellite images we arranged from NASA's Transition Region and Coronal Explorer (TRACE) reveal the onset of visibility of Venus's atmosphere and give further information about the black-drop effect, whose causes we previously demonstrated from TRACE observations of a transit of Mercury. The atmosphere is gradually revealed before second contact and after third contact, resulting from the changing depth of atmospheric layers refracting the photospheric surface into the observer's direction. We use Venus Express observations to relate the atmospheric arcs seen during the transit to the atmospheric structure of Venus. Finally, we relate the transit images to current and future exoplanet observations, providing a sort of ground truth showing an analog in our solar system to effects observable only with light curves in other solar systems with the Kepler and CoRoT missions and ground-based exoplanet-transit observations.

We have used images from the Advanced Camera for Surveys on the Hubble Space Telescope in Hα, and in the neighboring continuum, to produce flux-calibrated images of the large spiral galaxy M51 and the dwarf irregular NGC 4449. From these images, we have derived the absolute luminosities in Hα, the areas, and the positions with respect to the galactic centers as reference points of over 2600 H ii regions in M51 and over 270 H ii regions in NGC 4449. Using this database, we have derived luminosity–volume (L–V) relations for the regions in the two galaxies, showing that within the error limits these obey the equation L ∼ V^2/3, which differs from the linear relation expected for regions of constant uniform electron density. We briefly discuss possible models which would give rise to this behavior—notably models with strong density inhomogeneities within the regions. Plotting the luminosity functions for the two galaxies, we find a break in the slope for M51 at log(L) = 38.5 dex (units in erg s⁻¹) for M51 in good agreement with the previous ground-based study by Rand, and above this luminosity NGC 4449 also shows a sharp decline in its luminosity function, although the number of regions is too small to plot the function well at higher luminosities. The cumulative diameter distribution for the H ii regions of M51 shows dual behavior, with a break at a radius close to 100 pc, the radius of regions with the break luminosity. Here too we indicate possible physical implications.

We describe a new method which achieves high-precision very long baseline interferometry (VLBI) astrometry in observations at millimeter (mm) wavelengths. It combines fast frequency-switching observations, to correct for the dominant non-dispersive tropospheric fluctuations, with slow source-switching observations, for the remaining ionospheric dispersive terms. We call this method source-frequency phase referencing. Provided that the switching cycles match the properties of the propagation media, one can recover the source astrometry. We present an analytic description of the two-step calibration strategy, along with an error analysis to characterize its performance. Also, we provide observational demonstrations of a successful application with observations using the Very Long Baseline Array at 86 GHz of the pairs of sources 3C274 and 3C273 and 1308+326 and 1308+328 under various conditions. We conclude that this method is widely applicable to mm-VLBI observations of many target sources, and unique in providing bona fide astrometrically registered images and high-precision relative astrometric measurements in mm-VLBI using existing and newly built instruments, including space VLBI.

We present the results of a deep, wide-field CCD survey for the open cluster NGC 3532. Our new BV(RI)_c photometry effectively covers a one square degree area and reaches an unprecedented depth of V ∼ 21 to reveal that NGC 3532 is a rich open cluster that harbors a large number of faint, low-mass stars. We employ a number of methods to reduce the impact of field star contamination in the cluster color–magnitude diagrams (CMDs), including supplementing our photometry with JHK_s data from the 2MASS catalog. These efforts allow us to define a robust sample of candidate main-sequence stars suitable for a purely empirical determination of the cluster's parameters by comparing them to the well-established Hyades main sequence. Our results confirm previous findings that NGC 3532 lies fairly near to the Sun [(m − M)₀ = 8.46 ± 0.05; 492⁺¹²₋₁₁ pc] and has an extremely low reddening for its location near the Galactic plane [E(B − V) = 0.028 ± 0.006]. Moreover, an age of ∼300 Myr has been derived for the cluster by fitting a set of overshooting isochrones to the well-populated upper main sequence. This new photometry also extends faint enough to reach the cluster white dwarf sequence, as confirmed by our photometric recovery of eight spectroscopically identified members of the cluster. Using the location of these eight members, along with the latest theoretical cooling tracks, we have identified ∼30 additional white dwarf stars in the [V, (B − V)] CMD that have a high probability of belonging to NGC 3532. Reassuringly, the age we derive from fitting white dwarf isochrones to the locus of these stars, 300 ± 100 Myr, is consistent with the age derived from the turnoff. Our analysis of the photometry also includes an estimation of the binary star fraction as well as a determination of the cluster's luminosity and mass functions.

In this paper, we analyze new orbital elements, and quantities that can be derived from them, for six binaries. For four of them, WDS 00251+4803 = HDS 56, WDS 01071−0036 = HDS 144 AB, WDS 06426+3955 = HDS 930, and WDS 21014+4037 = HDS 2995, the orbital elements are calculated for the first time. For the other two, WDS 04195+3800 = HDS 552 and WDS 23209+1643 = HEI 88, the orbital elements are recalculated. Five binaries, denoted as HDS, were discovered during the Hipparcos mission while the remaining binary was discovered somewhat earlier. HEI 88 was measured for the first time in 1978. All studied pairs are close, with almost all measured separations less than 0.3 arcsec. For these binaries the observations were usually performed using the speckle-interferometric technique with the exception of HEI 88, which was observed visually on eight occasions. The resulting orbital periods fall within 13 and 69 years. In addition to the orbital elements, we also give (O–C) residuals in θ and ρ, masses, dynamical parallaxes, absolute magnitudes, spectral types, and ephemerides for the next five years.

We present 41 trigonometric parallaxes of 37 stellar systems, most of which have proper motions greater than 10 yr⁻¹. These are the first trigonometric parallaxes for 24 systems. Overall, there are 15 red dwarf systems and 22 red subdwarf systems in the sample. Five of the systems are multiples with directly detected companions, and we have discovered perturbations caused by unseen companions in two additional cases, the dwarf LHS 501 and the subdwarf LHS 440. The latter system may eventually provide important dynamical mass points on the subdwarf mass–luminosity relation. Two additional stars of note are LHS 272, the third closest M-type subdwarf at a distance of only 13.6 pc, and LHS 2734 AB, a high-velocity subdwarf binary with V_tan> 700 km s⁻¹, which likely exceeds the escape velocity of the Milky Way. We also report the first long-term variability study of cool subdwarfs indicating that cool subdwarfs are less photometrically variable than their main-sequence counterparts.

A new method was developed to estimate the effective temperature, surface gravity, and metallicity of cool stars using only photometric indices in the uvby color system. In a graphical method, T_eff and log g were determined for all of the different values of [Fe/H] using model atmosphere grids with respect to (b − y):c₁ and (b − y):m₁ pair indices. Then, a three-dimensional figure where X-, Y-, and Z-axes correspond to T_eff, log g, and [Fe/H] was produced. By reading an intersection of two curves formed by a connection of three parameters obtained from the (b − y):c₁ and (b − y):m₁ pair indices on each of the three projected planes, T_eff, log  g, and [Fe/H] were determined simultaneously. In addition, an analytical method was devised based on the same algorithm developed for the graphical method. The new method was applied to a number of field dwarfs and giants, and the results were compared with those from a spectroscopic method and other photometric calibrations.

The results of near-infrared imaging and spectroscopy of a substellar companion (SR12 C), with a possible planetary mass, of a binary T Tauri star (SR12 AB) in the ρ Ophiuchi star-forming region are presented. The object is separated by ∼87, corresponding to ∼1100 AU at 125 pc, and has an H-band brightness of 15.2 mag and infrared spectra suggesting a spectral type of M9.0 ± 0.5. It is confirmed that SR12 C is physically related to the ρ Ophiuchi star-forming region from its common proper motion with SR12 AB and its youth is confirmed by a gravity-sensitive spectral feature. Furthermore, based on the number of known members of the ρ Ophiuchi star-forming region in the area in which SR12 AB exists, the probability of a chance alignment is ∼1% and it is therefore likely that SR12 C is physically associated with SR12 AB. The mass of SR12 C is estimated by comparing its estimated luminosity and assumed age with the theoretical age–luminosity relation. SR12 C is identified as an extremely low-mass (0.013 ± 0.007 M_☉) object, but its separation from its parent star is the widest among planetary-mass companion (PMC) candidates imaged to date. In addition, SR12 C is the first PMC candidate directly imaged around a binary star. This discovery suggests that PMCs form via multiple star formation processes including disk gravitational instability and cloud core fragmentation.

P Cygni is a prototype of the luminous blue variables (or S Doradus variables), and the star displays photometric and emission line variability on a timescale of years (known as the "short S Doradus-phase" variations). Here we present new high-resolution Hα spectroscopy of P Cyg that we combine with earlier spectra and concurrent V-band photometry to document the emission and continuum flux variations over a 24 year time span. We show that the emission and continuum fluxes vary in concert on timescales of 1.6 years and longer, but differ on shorter timescales. The Hα profile shape also varies on the photometric timescales, and we describe the observed co-variations of the emission peak and absorption trough properties. We argue that the episodes of photometric and emission brightening are caused by increases in the size of the emission region that are related to variations in wind mass-loss rate and outflow speed. We find evidence of blueward accelerating, discrete absorption components (DACs) in the absorption trough of the Hα profile, and these features have slower accelerations and longer durations than those observed in other lines. The DAC strengths also appear to vary on the photometric timescales, and we suggest that the propagation of the DAC-related wind structures is closely related to changes in the overall wind mass-loss rate and velocity.

V446 Her is the best example of an old nova which has developed dwarf nova (DN) eruptions in the post-nova state. We report on observed properties of the long-term light curve of V446 Her, using photometry over 19 years. Yearly averages of the outburst (OB) magnitudes show a decline of ∼0.013 mag yr⁻¹, consistent with the decline of other post-novae that do not have DN OBs. Previous suggestions of bimodal distributions of the amplitudes and widths of the OBs are confirmed. The OBs occur at a mean spacing of 18 days but the range of spacings is large (13–30 days). From simulations of DN OBs, it has been predicted that the OB spacing in V446 Her will increase as $\dot{M}$ from the red dwarf companion slowly falls following the nova; however, the large intrinsic scatter in the spacings serves to hide any evidence of this effect. We do find a systematic change in the OB pattern in which the brighter, wider type of OBs disappeared after late 2003, and this phenomenon is suggested to be due to falling $\dot{M}$ following the nova.

We report on extensive photometry of DK Lac obtained during the interval 1990–2009, which includes a 2 mag low state during 2001–2003. Much of the photometry consists of exposures obtained with a typical spacing of several days, but also includes 26 sequences of continuous photometry each lasting 2–7 hr. We find no evidence for periodicities in our data. We do find that the random variations in the low state are approximately twice those in the high state, when expressed in magnitudes. The lack of orbital-timescale variations is attributed to the nearly face-on presentation of the disk. There is a 0.2 mag decline in the high-state brightness of the system over 19 years, which is consistent with the behavior of other old novae in the decades following outburst. High-state spectra are also presented and discussed. We find that the equivalent width of Hα falls by about double from 1991 to 2008. The photometric properties are discussed in the context of the hibernation scenario for the behavior of novae between outbursts, in which we conclude that low states in old novae are probably unrelated to their possible entrance into hibernation.

The properties of molecular clouds associated with 10 H ii regions were studied using CO observations. We identified 142 dense clumps within our sample and found that our sources are divided into two categories: those with clumps that show a power-law size–line-width relation (Type I) and those that do not show any relation (Type II). The clumps in the Type I sources have larger power-law indices than found in previous studies. The clumps in the Type II sources have larger line widths than do the clumps in the Type I sources. The mass M_LTE increases with ΔV for both ¹²CO and ¹³CO lines in Type I sources. No relation was found for Type II sources. Type II sources show evidence (such as outflows) of current active star formation within the clump and we suggest that the lack of a size–line-width relation is a sign of current active star formation. For both types of sources, no relation was found between volume density and size, but overall larger clumps have smaller volume density, indicating that smaller clumps are more evolved and have contracted to smaller sizes and higher densities. Massive clumps seem to have similar masses calculated by different methods but lower mass clumps have larger virial masses compared to velocity integrated (X-factor) and local thermodynamic equilibrium mass. We found no relation between mass distribution of the clumps and distance from the H ii region ionization front, but a weak decrease of the excitation temperature with increasing distance from the ionized gas. The clumps in collected shells around the H ii regions have slightly larger line widths but no relation was found between line width and distance from the H ii region, which probably indicates that the internal dynamics of the clumps are not affected by the ionized gas. Internal sources of turbulence, such as outflows and stellar winds from young proto-stars, may have a more important role on the molecular gas dynamics. We suggest that large line width and larger size–line-width power-law indices are therefore the initial characteristics of clumps in massive star-forming clouds (e.g., our Type I sources) and that some may evolve into objects similar to our Type II sources, where local "second generation" stars are forming and eliminating the size–line-width relation.

Using Doppler tomography we show that FS Aur-79, a near-contact close binary system with late-type active dK7e+dM3e components, has chromospheric prominences in two distinct emission regions associated with the primary star and a larger amount of chromospheric activity associated with the cooler secondary star. The line profiles, equivalent widths, and equivalent width ratios of the Hα and Hβ emission lines as a function of orbital phase further support that the majority of the chromospheric emission originates above the secondary star and near the neck region. Analysis of high-resolution spectra using the technique of broadening functions has enabled us to determine the radial velocity of the secondary star near quadratures to be approximately 224 km s⁻¹. A Wilson–Devinney model of the system fitting the UBV light curves and radial velocities shows that there are star spots near the chromospherically active regions. Finally, the absence of Li I λ6708 in the spectra lets us put a lower limit on the age of this system to at least 500 Myr.

In order to investigate the relationship between the local environment and the properties of natal star clusters, we obtained radio observations of 25 star-forming galaxies within 20 Mpc using the Very Large Array and the Australia Telescope Compact Array. Natal star-forming regions can be identified by their characteristic thermal radio emission, which is manifest in their spectral index at centimeter wavelengths. The host galaxies in our sample were selected based upon their likelihood of harboring young star formation. In star-forming regions, the ionizing flux of massive embedded stars powers the dominant thermal free–free emission of those sources, resulting in a spectral index of α ≳ −0.2 (where S_ν ∝ ν^α), which we compute. With the current sensitivity, we find that of the 25 galaxies in this sample only 5 have radio sources with spectral indices that are only consistent with a thermal origin, 4 have radio sources that are only consistent with a non-thermal origin, 6 have radio sources whose nature is ambiguous due to uncertainties in the spectral index, and 16 have no detected radio sources. For those sources that appear to be dominated by thermal emission, we infer the ionizing flux of the star clusters and the number of equivalent O7.5 V stars that are required to produce the observed radio flux densities. The most radio-luminous clusters that we detect have an equivalent of ∼7 × 10³ O7.5 V stars, and the smallest only have an equivalent of ∼10² O7.5 V stars; thus these star-forming regions span the range of large OB associations to moderate "super star clusters." With the current detection limits, we also place upper limits on the masses of clusters that could have recently formed; for a number of galaxies we can conclusively rule out the presence of natal clusters significantly more massive than the Galactic star-forming region W49A (∼5 × 10⁴M_☉). The dearth of current massive cluster formation in these galaxies suggests that either their current star formation intensities have fallen to near or below that of the Milky Way and/or the evolutionary state that gives rise to thermal radio emission is short-lived.

We show that star formation in the giant H ii region NGC 5471 has been ongoing during the past 100 Myr. Using Hubble Space Telescope/Wide-Field Planetary Camera 2 F547M and F675W, ground-based JHK_s, and GALEX FUV and NUV images, we have conducted a photometric study of the star formation history (SFH) in the massive giant extragalactic H ii region NGC 5471 in M101. We perform a photometric study of the color–magnitude diagram (CMD) of the resolved stars and an integrated analysis of the main individual star-forming clusters and of NGC 5471 as a whole. The integrated UV–optical–NIR photometry for the whole region provides two different reference ages, 8 Myr and 60 Myr, revealing a complex SFH, clearly confirmed by the CMD-resolved stellar photometry analysis. The spatial distribution of the stars shows that the star formation in NGC 5471 has proceeded along the whole region during, at least, the last 100 Myr. The current ionizing clusters are enclosed within a large bubble, which is likely to have been produced by the stars that formed in a major event ∼20 Myr ago.

We present new X-ray and far-ultraviolet (FUV) observations of T Tauri stars covering the age range 1–10 Myr. Our goals are to observationally constrain the intensity of radiation fields responsible for evaporating gas from the circumstellar disk and to assess the feasibility of current photoevaporation models, focusing on X-ray and UV radiation. We greatly increase the number of 7–10 Myr old T Tauri stars observed in X-rays by including observations of the well-populated 25 Ori aggregate in the Orion OB1a subassociation. With these new 7–10 Myr objects, we confirm that X-ray emission remains constant from 1 to 10 Myr. We also show, for the first time, observational evidence for the evolution of FUV radiation fields with a sample of 56 accreting and non-accreting young stars spanning 1 Myr to 1 Gyr. We find that the FUV emission decreases on timescales consistent with the decline of accretion in classical T Tauri stars until reaching the chromospheric level in weak T Tauri stars and debris disks. Overall, we find that the observed strength of high-energy radiation is consistent with that required by photoevaporation models to dissipate the disks in timescales of approximately 10 Myr. Finally, we find that the high-energy fields that affect gas evolution are not similarly affecting dust evolution; in particular, we find that disks with inner clearings, transitional disks, have similar levels of FUV emission as full disks.

SWAN, the Solar Wind ANisotropies all-sky hydrogen Lyα camera on the Solar and Heliospheric Observatory spacecraft that makes all-sky images of interplanetary neutral hydrogen, has an ongoing campaign to make special observations of comets, both short- and long-period ones, in addition to the serendipitous observations of comets as part of the all-sky monitoring program. We report here on a study of several short-period comets that were detected by SWAN: 21P/Giacobini-Zinner (1998 and 2005 apparitions), 19P/Borrelly (2001 apparition), 81P/Wild 2 (1997 apparition), and 103P/Hartley 2 (1997 apparition). SWAN observes comets over long continuous stretches of their visible apparitions and therefore provides excellent temporal coverage of the water production. For some of the observations we are also able to analyze an entire sequence of images over many days to several weeks/months using our time-resolved model and extract daily average water production rates over continuous periods of several days to months. The short-term (outburst) and long-term behavior can be correlated with other observations. The overall long-term variation is examined in light of seasonal effects seen in the pre- to post-perihelion differences. For 21P/Giacobini-Zinner and 81P/Wild 2 the activity variations over each apparition were more continuously monitored but nonetheless consistent with previous observations. For 19P/Borrelly we found a very steep variation of water production rates, again consistent with some previous observations, and a variation over six months around perihelion that was reasonably consistent with the spin-axis model of Schleicher et al. and the illumination of the main active areas. During the 1997–1998 apparition of 103P/Hartley 2, the target comet of the EPOXI mission (the Deep Impact extended mission), we found a variation with heliocentric distance (∼r^−3.6) that was almost as steep as 19P/Borrelly and, given the small measured radius near aphelion, this places a number of possible constraints on the size, shape, and/or distribution active of areas on the surface.

The Chandra Transmission Grating Data Archive and Catalog (TGCat) provides easy access to analysis-ready products, specifically, high-resolution X-ray count spectra and their corresponding calibrations. The web interface makes it easy to find observations of a particular object, type of object, or type of observation; to quickly assess the quality and potential usefulness of the spectra from pre-computed summary plots; or to customize a view with an interactive plotter, optionally combining spectra over multiple orders or observations. Data and responses can be downloaded as a package or as individual files, and the query results themselves can be retrieved as ASCII or Virtual Observatory tables. Portable reprocessing scripts used to create the archive and which use the Chandra X-ray Center's (CXC's) software and other publicly available software are also available, facilitating standard or customized reprocessing from Level 1 CXC archival data to spectra and responses with minimal user interaction.

The Hercules Thick Disk Cloud was initially discovered as an excess in the number of faint blue stars between Quadrants 1 and 4 of the Galaxy. The origin of the Cloud could be an interaction with the disk bar, a triaxial Thick Disk, or a merger remnant or stream. To better map the spatial extent of the Cloud along the line of sight, we have obtained multi-color UBVR photometry for 1.2 million stars in 63 fields each of approximately 1 deg². Our analysis of the fields beyond the apparent boundaries of the excess has already ruled out a triaxial Thick Disk as a likely explanation. In this paper, we present our results for the star counts over all of our fields, determine the spatial extent of the overdensity across and along the line of sight, and estimate the size and mass of the Cloud. Using photometric parallaxes, the stars responsible for the excess are between 1 and 6 kpc from the Sun, 0.5–4 kpc above the Galactic plane, and extend approximately 3–4 kpc across our line of sight. The Cloud is thus a major substructure in the Galaxy. The distribution of the excess along our sight lines corresponds with the density contours of the bar in the Disk, and its most distant stars are directly over the bar. We also see through the Cloud to its far side. Over the entire 500 deg² of the sky containing the Cloud, we estimate more than 5.6 million stars and 1.9 million solar masses of material. If the overdensity is associated with the bar, it would exceed 1.4 billion stars and more than 50 million solar masses. Finally, we argue that the Hercules–Aquila Cloud is actually the Hercules Thick Disk Cloud.

In the first two papers of this series, Larsen et al. describe our faint CCD survey in the inner Galaxy and map the overdensity of thick disk stars in Quadrant 1 (Q1) to 5 kpc or more along the line of sight. The regions showing the strongest excess are above the density contours of the bar in the Galactic disk. In this third paper on the asymmetric thick disk, we report on radial velocities and derived metallicity parameters for over 4000 stars in Q1, above and below the plane, and in Quadrant 4 (Q4) above the plane. We confirm the corresponding kinematic asymmetry first reported by Parker et al., extended to greater distances and with more spatial coverage. The thick disk stars in Q1 have a rotational lag of 60–70 km s⁻¹ relative to circular rotation, and the metal-weak thick disk stars have an even greater lag of 100 km s⁻¹. Both lag their corresponding populations in Q4 by ≈30 km s⁻¹. Interestingly, the disk stars in Q1 also appear to participate in the rotational lag by about 30 km s⁻¹. The enhanced rotational lag for the thick disk in Q1 extends to 4 kpc or more from the Sun. At 3–4 kpc, our sight lines extend above the density contours on the near side of the bar, and as our lines of sight pass directly over the bar the rotational lag appears to decrease. This is consistent with a "gravitational wake" induced by the rotating bar in the disk which would trap and pile up stars behind it. We conclude that a dynamical interaction with the stellar bar is the most probable explanation for the observed kinematic and spatial asymmetries.

We used the near-IR imager/spectrograph LUCIFER mounted on the Large Binocular Telescope to image, with subarcsecond seeing, the local dwarf starburst NGC 1569 in the JHK bands and He i 1.08 μm, [Fe ii] 1.64 μm, and Brγ narrowband filters. We obtained high-quality spatial maps of He i 1.08 μm, [Fe ii] 1.64 μm, and Brγ emission across the galaxy, and used them together with Hubble Space Telescope/Advanced Camera for Surveys images of NGC 1569 in the Hα filter to derive the two-dimensional spatial map of the dust extinction and surface star formation rate (SFR) density. We show that dust extinction (as derived from the Hα/Brγ flux ratio) is rather patchy and, on average, higher in the northwest (NW) portion of the galaxy (E_g(B − V) ≃ 0.71 mag) than in the southeast (E_g(B − V) ≃ 0.57 mag). Similarly, the surface density of SFR (computed from either the dereddened Hα or dereddened Brγ image) peaks in the NW region of NGC 1569, reaching a value of about 4 × 10⁻⁶ M_☉ yr⁻¹ pc⁻². The total SFR as estimated from the integrated, dereddened Hα (or, alternatively, Brγ) luminosity is about 0.4 M_☉ yr⁻¹, and the total supernova rate from the integrated, dereddened [Fe ii] 1.64 μm luminosity is about 0.005 yr⁻¹ (assuming a distance of 3.36 Mpc). The azimuthally averaged [Fe ii] 1.64 μm/Brγ flux ratio is larger at the edges of the central, gas-deficient cavities (encompassing the superstar clusters A and B) and in the galaxy outskirts. If we interpret this line ratio as the ratio between the average past star formation (as traced by supernovae) and ongoing activity (represented by OB stars able to ionize the interstellar medium), it would then indicate that star formation has been quenched within the central cavities and lately triggered in a ring around them. The number of ionizing hydrogen and helium photons as computed from the integrated, dereddened Hα and He i 1.08 μm luminosities suggests that the latest burst of star formation occurred about 4 Myr ago and produced new stars with a total mass of ≃1.8 × 10⁶ M_☉.

We present a statistical study of the correlations and dimensionality of emission lines carried out on a sample of over 40,000 Sloan Digital Sky Survey (SDSS) galaxies. Using principal component analysis, we found that the equivalent widths of the 11 strongest lines can be well represented using three parameters. We also explore correlations of the emission pattern with the eigenspace representation of the continuum spectrum. The observed relations are used to provide an empirical prescription for expectation values and variances of emission-line strengths as a function of spectral shape. We show that this estimation of emission lines has a sufficient accuracy to make it suitable for photometric applications. The method has already proved useful in SDSS photometric redshift estimation.

Using Hubble Space Telescope images of 119 young planetary nebulae (PNs), most of which have not previously been published, we have devised a comprehensive morphological classification system for these objects. This system generalizes a recently devised system for pre-planetary nebulae, which are the immediate progenitors of PNs. Unlike previous classification studies, we have focused primarily on young PNs rather than all PNs, because the former best show the influences or symmetries imposed on them by the dominant physical processes operating at the first and primary stage of the shaping process. Older PNs develop instabilities, interact with the ambient interstellar medium, and are subject to the passage of photoionization fronts, all of which obscure the underlying symmetries and geometries imposed early on. Our classification system is designed to suffer minimal prejudice regarding the underlying physical causes of the different shapes and structures seen in our PN sample, however, in many cases, physical causes are readily suggested by the geometry, along with the kinematics that have been measured in some systems. Secondary characteristics in our system, such as ansae, indicate the impact of a jet upon a slower-moving, prior wind; a waist is the signature of a strong equatorial concentration of matter, whether it be outflowing or in a bound Keplerian disk, and point symmetry indicates a secular trend, presumably precession, in the orientation of the central driver of a rapid, collimated outflow.

In 2009, we used the Subaru telescope to observe all the faint irregular satellites of Neptune for the first time since 2004. These observations extend the data arcs for Halimede, Psamathe, Sao, Laomedeia, and Neso from a few years to nearly a decade. We also report on a search for unknown Neptune satellites in a half-square degree of sky and a limiting magnitude of 26.2 in the R band. No new satellites of Neptune were found. We numerically integrate the orbits for the five irregulars and summarize the results of the orbital fits in terms of the state vectors, post-fit residuals, and mean orbital elements. Sao and Neso are confirmed to be Kozai librators, while Psamathe is a "reverse circulator." Halimede and Laomedeia do not seem to experience any strong resonant effects.

We present new results from a ground-based program to determine the proper motion of the Magellanic Clouds (MCs) relative to background quasars (QSOs), being carried out with the Iréneé du Pont 2.5 m telescope at Las Campanas Observatory, Chile. The data were secured over a time base of seven years and with eight epochs of observation "As measured" (field) proper motions were obtained for five QSO fields in the Small Magellanic Cloud (SMC): QJ0033−7028, QJ0035−7201, QJ0047−7530, QJ0102−7546, and QJ0111−7249. Assuming that the SMC has a disklike central structure, but that it does not rotate, we determined a center-of-mass (CM) proper motion for the SMC from two of these fields, QJ0033−7028 and QJ0035−7201, located to the northwest and west of the main body of the SMC, respectively. Combining these latter proper motions with the CM proper motion presented by Costa et al. (hereafter CMP09) for the SMC (from the field QJ0036−7227, located to the west of the main body of the SMC), we obtain a weighted mean of μ_α cos δ = +0.93 ± 0.14 mas yr⁻¹ and μ_δ = −1.25 ± 0.11 mas yr⁻¹. This CM proper motion is in good agreement with recent results by Piatek et al. and Vieira et al., and we are confident that it is a good representation of the "bulk" transverse motion of the SMC. On the contrary, the results we obtain from the fields QJ0047−7530 and QJ0102−7546, located to the south of the main body of the SMC, and the field QJ0111−7249, located to the east of its main body, seem to be affected by streaming motions. For this reason, we have not used the latter to determine the SMC CM proper motion. These streaming motions could be evidence that the SMC was tidally disrupted in a close encounter with the Large Magellanic Cloud (LMC). Complementing the SMC CM proper motions given here and in CMP09, with the currently accepted radial velocity of its center, we have derived its galactocentric (gc) velocity components, obtaining a weighted mean of V_gc,t = +289 ± 25 km s⁻¹ and V_gc,r = +14 ± 24 km s⁻¹. These velocities, together with the galactocentric velocity components given for the LMC in CMP09, imply a relative velocity between the LMC and SMC of 67 ± 42 km s⁻¹ for V_rot,LMC = 50 km s⁻¹ and of 98 ± 48 km s⁻¹ for V_rot,LMC = 120 km s⁻¹. Despite our large errors, these values are consistent with the standard assumption that the MCs are gravitationally bound to each other.

We present a catalog of intervening Mg ii quasar absorption-line systems in the redshift interval 0.36 ⩽ z ⩽ 2.28. The catalog was built from Sloan Digital Sky Survey Data Release Four (SDSS DR4) quasar spectra. Currently, the catalog contains ∼17, 000 measured Mg ii doublets. We also present data on the ∼44, 600 quasar spectra which were searched to construct the catalog, including redshift and magnitude information, continuum-normalized spectra, and corresponding arrays of redshift-dependent minimum rest equivalent widths detectable at our confidence threshold. The catalog is available online. A careful second search of 500 random spectra indicated that, for every 100 spectra searched, approximately one significant Mg ii system was accidentally rejected. Current plans to expand the catalog beyond DR4 quasars are discussed. Many Mg ii absorbers are known to be associated with galaxies. Therefore, the combination of large size and well understood statistics makes this catalog ideal for precision studies of the low-ionization and neutral gas regions associated with galaxies at low to moderate redshift. An analysis of the statistics of Mg ii absorbers using this catalog will be presented in a subsequent paper.

We present the results of a study of differential rotation on the K2 IV primary of the RS CVn binary II Pegasi (HD 224085) performed by inverting light curves to produce images of the dark starspots on its surface. The data were obtained in the standard Johnson B and V filter passbands via the Tennessee State University T3 0.4 m Automated Photometric Telescope from JD 2447115.8086–2455222.6238 (1987 November 16–2010 January 26). The observations were subdivided into 79 data sets consisting of pairs of B and V light curves, which were then inverted using a constrained nonlinear inversion algorithm that makes no a priori assumptions regarding the number of spots or their shapes. The resulting surface images were then assigned to 24 groups corresponding to time intervals over which we could observe the evolution of a given group of spots (except for three groups consisting of single data sets). Of these 24 groups, six showed convincing evidence of differential rotation over time intervals of several months. For the others, the spot configuration was such that differential rotation was neither exhibited nor contraindicated. The differential rotation we infer is in the same sense as that on the Sun: lower latitudes have shorter rotation periods. From plots of the range in longitude spanned by the spotted regions versus time, we obtain estimates of the differential rotation coefficient k defined as in earlier work by Henry et al. and show that our results for its value are consistent with the value obtained therein.

We present a 1.1 mm map of the Braid Nebula star formation region in Cygnus OB7 taken using Bolocam on the Caltech Submillimeter Observatory. Within the 1 deg² covered by the map, we have detected 55 cold dust clumps all of which are new detections. A number of these clumps are coincident with IRAS point sources although the majority are not. Some of the previously studied optical/near-IR sources are detected at 1.1 mm. We estimate total dust/gas masses for the 55 clumps together with peak visual extinctions. We conclude that over the whole region, approximately 20% of the clumps are associated with IRAS sources suggesting that these are protostellar objects. The remaining 80% are classed as starless clumps. In addition, both FU Orionis (FUor) like objects in the field, the Braid Star and HH 381 IRS, are associated with strong millimeter emission. This implies that FUor eruptions can occur at very early stages of pre-main-sequence life. Finally, we determine that the cumulative clump mass function for the region is very similar to that found in both the Perseus and ρ Ophiuchus star-forming regions.

We report the discovery that the star V474 Car is an extremely active, high velocity halo RS CVn system. The star was originally identified as a possible pre-main-sequence star in Carina, given its enhanced stellar activity, rapid rotation (10.3 days), enhanced Li, and absolute magnitude which places it above the main sequence (MS). However, its extreme radial velocity (264 km s⁻¹) suggested that this system was unlike any previously known pre-MS system. Our detailed spectroscopic analysis of echelle spectra taken with the CTIO 4 m finds that V474 Car is both a spectroscopic binary with an orbital period similar to the photometric rotation period and metal-poor ([Fe/H] ≃−0.99). The star's Galactic orbit is extremely eccentric (e ≃ 0.93) with a perigalacticon of only ∼0.3 kpc of the Galactic center—and the eccentricity and smallness of its perigalacticon are surpassed by only ∼0.05%  of local F/G-type field stars. The observed characteristics are consistent with V474 Car being a high-velocity, metal-poor, tidally locked, chromospherically active binary, i.e., a halo RS CVn binary, and one of only a few such specimens known.

We have obtained high spatial resolution Keck OSIRIS integral field spectroscopy of four z ∼ 1.5 ultra-luminous infrared galaxies that exhibit broad Hα emission lines indicative of strong active galactic nucleus (AGN) activity. The observations were made with the Keck laser guide star adaptive optics system giving a spatial resolution of 01 or <1 kpc at these redshifts. These high spatial resolution observations help to spatially separate the extended narrow-line regions—possibly powered by star formation—from the nuclear regions, which may be powered by both star formation and AGN activity. There is no evidence for extended, rotating gas disks in these four galaxies. Assuming dust correction factors as high as A(Hα) = 4.8 mag, the observations suggest lower limits on the black hole masses of (1–9) × 10⁸ M_☉ and star formation rates <100 M_☉ yr⁻¹. The black hole masses and star formation rates of the sample galaxies appear low in comparison to other high-z galaxies with similar host luminosities. We explore possible explanations for these observations, including host galaxy fading, black hole growth, and the shut down of star formation.