Search

We present the final results of an imaging and spectroscopic search for stars in the Large Magellanic Cloud (LMC) with C II 7231, 7236 emission lines. The goal is to identify and study [WC11] stars, the coolest of the low-mass Wolf-Rayet sequence, and a subset of central stars of planetary nebulae where the C II lines are known to be especially prominent. A recent serendipitous discovery of an LMC [WC11] raised the possibility that these objects, although difficult to identify, might in fact be more common than previously believed. Several new members of this rare class have been found in this survey. It now seems clear, however, that a significant number of these stars are not hiding amongst the general [WC] population. We point out that the C II doublet intensity ratio observed in our spectra proves to neatly divide the objects into two distinct groups, with the C II emission likely originating from either the stellar wind or a surrounding nebula. The physics of the C II emission mechanism correctly explains this bifurcation. Spectral subtypes are suggested for most of the objects. The numerous spectroscopic clues now available for these objects should facilitate future detailed modeling., Accepted for publication in The Astrophysical Journal

We present a narrow-band imaging survey of the Large Magellanic Cloud, designed to isolate the C II $\lambda\lambda$7231, 7236 emission lines in objects as faint as $m_{\lambda7400}\sim18$. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by C II emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged $\sim$50$~$deg$^2$ using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known C II emitters were easily recovered, validating the survey design. We find 38 new C II emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding C II emission in each. One is a new [WC11]. Another shows both the narrow C II emission lines characteristic of a [WC11], but also broad emission of C IV, O V, and He II characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak C II emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous O II transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected C II emitters are largely of an old population., Comment: Accepted for publication in the Astrophysical Journal, 2020

Identifications of a large fraction of previously unidentified lines in the complex spectrum of the low mass, late-type LMC [WC11] star J060819.93-715737.4 have been made utilizing electronic databases. There are an exceptionally large number of C II emission lines originating from autoionizing (ai) levels. Resonance fluorescence between the C II ground state and excited ai levels is shown to be a important photoabsorption process that is competitive with dielectronic recombination in exciting ai emission lines in stellar winds, and has broad application to many types of emission-line stars. In addition, numerous C II quartet multiplets appear in emission that are not excited directly by recombination or resonance fluorescence, signifying high wind densities in the emission region that enhance collisional transfer between doublet and quartet states., Comment: 17 pages, 1 figure, 1 table. Accepted for publication in ApJ

We report the serendipitous discovery of an object, UVQS J060819.93-715737.4, with a spectrum dominated by extremely intense, narrow C II emission lines. The spectrum is similar to those of the very rare, late-type [WC11] low-mass Wolf-Rayet stars. Despite the recognition of these stars as a distinct class decades ago, there remains barely a handful of Galactic members, all of which are also planetary-nebula central stars. Although no obvious surrounding nebulosity is present in J0608, [O II], [N II], and [S II] emission suggest the presence of an inconspicuous, low-excitation nebula. There is low-amplitude incoherent photometric variability on timescales of days to years, as well as numerous prominent P Cygni profiles, implying mass loss. There are indications of a binary companion. The star is located on the outskirts of the LMC, and the observed radial velocity (~250 km/s) and proper motion strongly suggest membership. If indeed an LMC member, this is the first extragalactic late [WC] star, and the first with an accurately determined luminosity, as the Galactic examples are too distant for precise parallax determinations. A high-quality, broad-coverage spectrum of the prototype of the late [WC] class, CPD -56 8032, is also presented. We discuss different excitation mechanisms capable of producing the great strength of the C II emission. Numerous autoionizing levels of C II are definitely populated by processes other than dielectronic recombination. Despite the spectacular emission spectra, observational selection makes objects such as these difficult to discover. Members of the [WC11] class may in fact be considerably more common than the handful of previously known late [WC] stars., Comment: Accepted for publication in The Astrophysical Journal

Wolf 1465 has been suggested as a candidate for a bright dwarf carbon star. It is not.

Although dwarf carbon (dC) stars are thought universally to be binaries to explain the presence of $C_2$ in their spectra while still near main sequence luminosity, direct observational evidence for binarity is remarkably scarce. Here we report the detection of a 2.92 d periodicity in both photometry and radial velocity of SDSS J125017.90+252427.6, an $r=16.4$ dC star. This is the first photometric binary dC, and only the second dC spectroscopic binary. The relative phase of the photometric period to the spectroscopic observations suggests that the photometric variations are a reflection effect due to heating from an unseen companion. The observed radial velocity amplitude of the dC component ($K = 98.8\pm10.7$ km/s) is consistent with a white dwarf companion, presumably the evolved star that earlier donated the carbon to the dC, although substantial orbital evolution must have occurred. Large synoptic photometric surveys such as the Palomar Transient Factory, used for this work, may prove useful for identifying binaries among the shorter period dC stars., Accepted for publication in The Astrophysical Journal (Letters)

The dwarf carbon (dC) star SDSS J112801.67+004034.6 has an unusually high radial velocity, 531$\pm 4$ km s$^{-1}$. We present proper motion and new spectroscopic observations which imply a large Galactic rest frame velocity, 425$\pm 9$ km s$^{-1}$. Several other SDSS dC stars are also inferred to have very high galactocentric velocities, again each based on both high heliocentric radial velocity and also confidently detected proper motions. Extreme velocities and the presence of $C_2$ bands in the spectra of dwarf stars are both rare. Passage near the Galactic center can accelerate stars to such extreme velocities, but the large orbital angular momentum of SDSS J1128 precludes this explanation. Ejection from a supernova in a binary system or disruption of a binary by other stars are possibilities, particularly as dC stars are thought to obtain their photospheric $C_2$ via mass transfer from an evolved companion., Comment: Accepted for publication in The Astrophysical Journal

An incidental spectrum of the poorly studied long period variable EF Aquilae shows [O III] emission indicative of a symbiotic star. Strong GALEX detections in the UV reinforce this classification, providing overt evidence for the presence of the hot subluminous companion. Recent compilations of the photometric behavior strongly suggest that the cool component is a Mira variable. Thus EF Aql appears to be a member of the rare symbiotic Mira subgroup., Accepted for publication in Publications of the Astronomical Society of the Pacific, Volume 128 (2016)

This paper describes the Seventh Data Release of the Sloan Digital Sky Survey (SDSS), marking the completion of the original goals of the SDSS and the end of the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most of the roughly 2000 deg^2 increment over the previous data release lying in regions of low Galactic latitude. The catalog contains five-band photometry for 357 million distinct objects. The survey also includes repeat photometry over 250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A coaddition of these data goes roughly two magnitudes fainter than the main survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2 in the Northern Galactic Cap, closing the gap that was present in previous data releases. There are over 1.6 million spectra in total, including 930,000 galaxies, 120,000 quasars, and 460,000 stars. The data release includes improved stellar photometry at low Galactic latitude. The astrometry has all been recalibrated with the second version of the USNO CCD Astrograph Catalog (UCAC-2), reducing the rms statistical errors at the bright end to 45 milli-arcseconds per coordinate. A systematic error in bright galaxy photometr is less severe than previously reported for the majority of galaxies. Finally, we describe a series of improvements to the spectroscopic reductions, including better flat-fielding and improved wavelength calibration at the blue end, better processing of objects with extremely strong narrow emission lines, and an improved determination of stellar metallicities. (Abridged), Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor corrections

We present a large sample of 501 radio-selected BL Lac candidates from the combination of the Sloan Digital Sky Survey (SDSS) Data Release 5 optical spectroscopy and from the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio survey; this is one of the largest BL Lac samples yet assembled, and each object emerges with homogeneous data coverage. Each candidate is detected in the radio from FIRST and confirmed in SDSS optical spectroscopy to have: (1) no emission feature with measured rest equivalent width larger than 5 Angstroms; and (2) no measured Ca II H/K depression larger than 40%. We subdivide our sample into 426 higher confidence candidates and 75 lower confidence candidates. We argue that contamination from other classes of objects that formally pass our selection criteria is small, and we identify a few very rare radio AGN with unusual spectra that are probably related to broad absorption line quasars. About one-fifth of our sample were known BL Lacs prior to the SDSS. A preliminary analysis of the sample generally supports the standard beaming paradigm. While we recover sizable numbers of low-energy and intermediate-energy cutoff BL Lacs (LBLs and IBLs, respectively), there are indications of a potential bias toward recovering high-energy cutoff BL Lacs (HBLs) from SDSS spectroscopy. Such a large sample may eventually provide new constraints on BL Lac unification models and their potentially peculiar cosmic evolution; in particular, our sample contains a significant number of higher redshift objects, a sub-population for which the standard paradigm has yet to be rigorously constrained.

We describe further results of a program aimed at yielding ∼104 fully characterized optical identifications of ROSAT X-ray sources. Our program employs X-ray data from the ROSAT All Sky Survey (RASS) and both optical imaging and spectroscopic data from the Sloan Digital Sky Survey (SDSS). RASS/SDSS data from 5740 deg2 of sky spectroscopically covered in SDSS Data Release 5 provide an expanded catalog of 7000 confirmed quasars and other active galactic nuclei (AGNs) that are probable RASS identifications. Again, in our expanded catalog the identifications as X-ray sources are statistically secure, with only a few percent of the SDSS AGNs likely to be randomly superposed on unrelated RASS X-ray sources. Most identifications continue to be quasars and Seyfert 1 galaxies with 15 < m < 21 and 0.01 < z < 4, but the total sample size has grown to include very substantial numbers of even quite rare AGNs, e.g., it now includes several hundreds of candidate X-ray-emitting BL Lac objects and narrow-line Seyfert 1 galaxies. In addition to exploring rare subpopulations, such a large total sample may be useful when considering correlations between the X-ray and the optical and may also serve as a resource list from which to select the "best" object (e.g., X-ray-brightest AGN of a certain subclass at a preferred redshift or luminosity) for follow-up X-ray spectral or alternate detailed studies.

AM CVn systems are a rare (about a dozen previously known) class of cataclysmic variables, arguably encompassing the shortest orbital periods (down to about 10 minutes) of any known binaries. Both binary components are thought to be degenerate (or partially so), likely with mass-transfer from a helium-rich donor onto a white dwarf, driven by gravitational radiation. Although rare, AM CVn systems are of high interest as possible SN Ia progenitors, and because they are predicted to be common sources of gravity waves in upcoming experiments such as LISA. We have identified four new AM CVn candidates from the Sloan Digital Sky Survey (SDSS) spectral database. All four show hallmark spectroscopic characteristics of the AM CVn class: each is devoid of hydrogen features, and instead shows a spectrum dominated by helium. All four show double-peaked emission, indicative of helium-dominated accretion disks. Limited time-series CCD photometric follow-on data have been obtained for three of the new candidates from the ARC 3.5m; most notably, a 28.3 minute binary period with sharp, deep eclipses is discovered in one case, SDSS J0926+3624. This is the first confirmed eclipsing AM CVn, and our data allow initial estimates of binary parameters for this ultracompact system. The four new SDSS objects also provide a substantial expansion of the currently critically-small sample of AM CVn systems.

We present a sample of 386 BL Lacertae (BL Lac) candidates identified from 2860 deg^2 of the Sloan Digital Sky Survey (SDSS) spectroscopic database. The candidates are primarily selected to have quasi-featureless optical spectra and low proper motions as measured from SDSS and USNO-B positions; however, our ability to separate Galactic from extragalactic quasi-featureless objects (QFOs) on the basis of proper motion alone is limited by the lack of reliable proper motion measurements for faint objects. Fortunately, high proper motion QFOs, mostly DC white dwarfs, populate a well defined region of color space, approximately corresponding to blackbodies with temperatures in the range 7000-12000 K. QFOs with measurable redshifts or X-ray or radio counterparts (i.e., evidence of an extragalactic/AGN nature) loosely follow a track in color space that corresponds to power-law continua plus host galaxy starlight, with typical power-law slopes in the range 1, Comment: 42 pages, 11 figures (4 in color), uses aastex.cls. To appear in the June 2005 edition of AJ. Full tables are temporarily available from http://www.astro.princeton.edu/~collinge/sdss_bllac/ and will be published electronically. Summary of changes: 1) improved SDSS/USNO-B proper motion treatment; 2) improved discussion of multiwavelength properties

This paper describes the Third Data Release of the Sloan Digital Sky Survey (SDSS). This release, containing data taken up through June 2003, includes imaging data in five bands over 5282 deg^2, photometric and astrometric catalogs of the 141 million objects detected in these imaging data, and spectra of 528,640 objects selected over 4188 deg^2. The pipelines analyzing both images and spectroscopy are unchanged from those used in our Second Data Release., 14 pages, including 2 postscript figures. Submitted to AJ. Data available at http://www.sdss.org/dr3

There are extraordinarily few far ultraviolet observations of RR Lyrae stars in the literature. We present Hubble Space Telescope FUV (~1600 A) imaging of the core of the globular cluster NGC 1851. Eleven new variables whose light curves are consistent with those of RR Lyr stars are discovered, increasing the total number of RR Lyr known in this cluster by a substantial amount. In agreement with basic physical theory, the observed amplitude of the variables in the FUV is enormous compared with the century of past optical observations, ranging up to 4 mag. HST STIS FUV observations of cluster cores may prove an especially effective means of obtaining a near-complete census of RR Lyr stars, combining high angular resolution, suppression of luminous red stars, and data where the stellar pulsation amplitudes are greatly enhanced. Attention is also drawn to a peculiar blue object in the cluster that is most probably a low mass x-ray binary system in quiescence., Accepted for publication in The Astronomical Journal, Vol. 128, Nov. 2004, 13 pages, 4 figures, AASTeX v5.0

The Sloan Digital Sky Survey has validated and made publicly available its Second Data Release. This data release consists of 3324 square degrees of five-band (u g r i z) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars and calibrating blank sky patches selected over 2627 degrees of this area, and tables of measured parameters from these data. The imaging data reach a depth of r ~ 22.2 (95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 milli-arcsec rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point spread function (PSF) magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 A to 9200 A at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars, and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines, and included in the Second Data Release. The data are publically available as of 2004 March 15 via the web sites http://www.sdss.org/dr2 and http://skyserver.sdss.org ., 24 pages, submitted to AJ. See ftp://ftp.astro.princeton.edu/strauss/sdss/dr2.ps for high-resolution figures

A search of more than 3,000 square degrees of high latitude sky by the Sloan Digital Sky Survey has yielded 251 faint high-latitude carbon stars (FHLCs), the large majority previously uncataloged. We present homogeneous spectroscopy, photometry, and astrometry for the sample. The objects lie in the 15.6 < r < 20.8 range, and exhibit a wide variety of apparent photospheric temperatures, ranging from spectral types near M to as early as F. Proper motion measurements for 222 of the objects show that at least 50%, and quite probably more than 60%, of these objects are actually low luminosity dwarf carbon (dC) stars, in agreement with a variety of recent, more limited investigations which show that such objects are the numerically dominant type of star with C_2 in the spectrum. This SDSS homogeneous sample of ~110 dC stars now constitutes 90% of all known carbon dwarfs, and will grow by another factor of 2-3 by the completion of the Survey. As the spectra of the dC and the faint halo giant C stars are very similar (at least at spectral resolution of 1,000) despite a difference of 10 mag in luminosity, it is imperative that simple luminosity discriminants other than proper motion be developed. We use our enlarged sample of FHLCs to examine a variety of possible luminosity criteria, including many previously suggested, and find that, with certain important caveats, JHK photometry may segregate dwarfs and giants., Accepted for publication in The Astronomical Journal, Vol. 127, May 2004, 37 pages, 12 figures

We discuss 18 white dwarfs, one of which (G227-5) was previously known, whose SDSS spectra show lines of neutral and/or singly ionized carbon. At least two and perhaps four show lines of neutral or singly ionized oxygen. Apart from the extremely hot PG 1159 stars, these are the first white dwarfs with photospheric oxygen detected in their optical spectra. The photometry strongly suggests that these stars lie in the 11,000–30,000 K temperature range of the helium-atmosphere DB white dwarfs, though only one of them shows weak neutral helium lines in the spectrum. Trigonometric parallaxes are known for G227-5 and another, previously known white dwarf (G35-26) showing atomic carbon lines, and they indicate that both are massive stars. Theoretical arguments suggest that all members of this class of rare white dwarfs are massive (~1 M⊙), and this finding could explain the paucity of massive DB white dwarfs.

The first full year of operation following the commissioning year of the Sloan Digital Sky Survey has revealed a wide variety of newly discovered cataclysmic variables. We show the SDSS spectra of forty-two cataclysmic variables observed in 2002, of which thirty-five are new classifications, four are known dwarf novae (CT Hya, RZ Leo, T Leo and BZ UMa), one is a known CV identified from a previous quasar survey (Aqr1) and two are known ROSAT or FIRST discovered CVs (RX J09445+0357, FIRST J102347.6+003841). The SDSS positions, colors and spectra of all forty-two systems are presented. In addition, the results of follow-up studies of several of these objects identify the orbital periods, velocity curves and polarization that provide the system geometry and accretion properties. While most of the SDSS discovered systems are faint (>18th mag) with low accretion rates (as implied from their spectral characteristics), there are also a few bright objects which may have escaped previous surveys due to changes in the mass transfer rate.

We present HST UV observations of the high-inclination low mass X-ray binary AC211 (X2127+119), which is located in the globular cluster M15 (NGC 7078). We have discovered a C P Cygni profile in this system, which confirms the existence of an outflow from AC211. The outflow velocity as measured from the P Cygni profile is � 1500 km s −1 .W e calculate that the mass lost through this wind is too small to support a large period derivative as favoured by Homer & Charles (1998). Using new X-ray observations we have revised the ephemeris for AC211 and we find no evidence in support of a period derivative. The UV spectrum exhibits several absorption features due to O, Si and C. The very strong He line at 1640 A is not seen to modulate strongly with orbital phase, suggesting its origin lies in the outer parts of the system. In contrast, the eclipse of the UV continuum is short compared with the X-ray and optical eclipses.

We know from observations that globular clusters are very efficient catalysts in forming unusual short-period binary systems or their offspring, such as low-mass X-ray binaries (LMXBs; neutron stars accreting matter from low-mass stellar companions), cataclysmic variables (CVs; white dwarfs accreting matter from stellar companions), and millisecond pulsars (MSPs; rotating neutron stars with spin periods of a few ms). Although there has been little direct evidence, the overabundance of these objects in globular clusters has been attributed by numerous authors to the high densities in the cores, which leads to an increase in the formation rate of exotic binary systems through close stellar encounters. Many such close binary systems emit X-radiation at low luminosities (L_x < 10^{34} erg/s) and are being found in large numbers through observations with the Chandra X-ray Observatory. Here we present conclusive observational evidence for a link between the number of close binaries observed in X-rays in a globular cluster and the stellar encounter rate of the cluster. We also make an estimate of the total number of LMXBs in globular clusters in our Galaxy., 11 pages, 1 b&w figure, 1 color figure

We have obtained Hubble Space Telescope/Space Telescope Imaging Spectrograph low-resolution ultraviolet spectra of the X-ray pulsar 4U 1626-67 (=KZ TrA); 4U 1626-67 is unusual even among X-ray pulsars because of its ultrashort binary period (P = 41.4 minutes) and remarkably low mass function (≤1.3 × 10-6 M⊙). The far-UV spectrum was exposed for a total of 32 ks and has sufficient signal-to-noise ratio to reveal numerous broad emission and prominent narrower absorption lines. Most of the absorption lines are consistent in strength with a purely interstellar origin. However, there is evidence that both C I and C IV require additional absorbing gas local to the system. In emission, the usual prominent lines of N V and He II are absent, while both O IV and O V are relatively strong. We further identify a rarely seen feature at ~1660 A as the O III] multiplet. Our ultraviolet spectra therefore provide independent support for the recent suggestion that the mass donor is the chemically fractionated core of either a CONe or ONeMg white dwarf; this was put forward to explain the results of Chandra high-resolution X-ray spectroscopy. The velocity profiles of the ultraviolet lines are in all cases broad and/or flat topped or perhaps even double peaked for the highest ionization cases of O; in either case, the ultraviolet line profiles are in broad agreement with the Doppler pairs found in the X-ray spectra. Both the X-ray and far-UV lines are plausibly formed in (or in an corona just above) a Keplerian accretion disk; the combination of ultraviolet and X-ray spectral data may provide a rich data set for follow-on detailed models of the disk dynamics and ionization structure in this highly unusual low-mass X-ray pulsar system.

We report on the Chandra ACIS-S3 imaging observation of the globular cluster NGC 6752. We detect 6 X-ray sources within the 10.5" core radius and 13 more within the 115" half-mass radius down to a limiting luminosity of Lx approx 10^{30} erg/s for cluster sources. We reanalyze archival data from the Hubble Space Telescope and the Australia Telescope Compact Array and make 12 optical identifications and one radio identification. Based on X-ray and optical properties of the identifications, we find 10 likely cataclysmic variables (CVs), 1-3 likely RS CVn or BY Dra systems, and 1 or 2 possible background objects. Of the 7 sources for which no optical identifications were made, we expect that ~2-4 are background objects and that the rest are either CVs or some or all of the five millisecond pulsars whose radio positions are not yet accurately known. These and other Chandra results on globular clusters indicate that the dozens of CVs per cluster expected by theoretical arguments are being found. The findings to date also suggest that the ratio of CVs to other types of X-ray sources is remarkably similar in clusters of very different structural parameters.

The commissioning year of the Sloan Digital Sky Survey has demonstrated that many cataclysmic variables have been missed in previous surveys with brighter limits. We report the identification of 22 cataclysmic variables, of which 19 are new discoveries and 3 are known systems (SW UMa, BH Lyn and Vir4). A compendium of positions, colors and characteristics of these systems obtained from the SDSS photometry and spectroscopy is presented along with data obtained during follow-up studies with the Apache Point Observatory (APO) and Manastash Ridge Observatory (MRO) telescopes. We have determined orbital periods for 3 of the new systems: two show dwarf nova outbursts, and the third is a likely magnetic system with eclipses of its region of line emission. Based on these results, we expect the completed survey to locate at least 400 new CVs. Most of these will be faint systems with low accretion rates that will provide new constraints on binary evolution models.

The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of ≈106 galaxies, 100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001 June, the SDSS released to the general astronomical community its early data release, roughly 462 deg2 of imaging data including almost 14 million detected objects and 54,008 follow-up spectra. The imaging data were collected in drift-scan mode in five bandpasses (u, g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2, 22.2, 21.3, and 20.5, respectively. The photometric calibration is reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are flux- and wavelength-calibrated, with 4096 pixels from 3800 to 9200 A at R ≈ 1800. We present the means by which these data are distributed to the astronomical community, descriptions of the hardware used to obtain the data, the software used for processing the data, the measured quantities for each observed object, and an overview of the properties of this data set.

We report on PTF1 J191905.19+481506.2, a newly discovered, partially eclipsing, outbursting AM CVn system found in the Palomar Transient Factory synoptic survey. This is only the second known eclipsing AM CVn system. We use high-speed photometric observations and phase-resolved spectroscopy to establish an orbital period of 22.4559(3) min. We also present a long-term light curve and report on the normal and super-outbursts regularly seen in this system, including a super-outburst recurrence time of 36.8(4) d. We use the presence of the eclipse to place upper and lower limits on the inclination of the system and discuss the number of known eclipsing AM CVn systems versus what would be expected., 13 pages, 10 figures, accepted to ApJ

KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among the brightest active galaxies monitored by the Kepler mission. We have carried out a reverberation mapping campaign designed to measure the broad-line region size and estimate the mass of the black hole in this galaxy. We obtained 74 epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m telescope from February to November of 2012, and obtained complementary V-band images from five other ground-based telescopes. We measured the H-beta light curve lag with respect to the V-band continuum light curve using both cross-correlation techniques (CCF) and continuum light curve variability modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53 (+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s. Combining these two results and assuming a virial scale factor of f = 5.13, we obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also obtained consistent but slightly shorter emission-line lags with respect to the Kepler light curve. Thanks to the Kepler mission, the light curve of KA1858+4850 has among the highest cadences and signal-to-noise ratios ever measured for an active galactic nucleus; thus, our black hole mass measurement will serve as a reference point for relations between black hole mass and continuum variability characteristics in active galactic nuclei.

Despite the unique X-ray behavior of the compact bursting X-ray source MXB 1730-335, the "Rapid Burster" (RB) in the highly reddened globular cluster Liller 1, to date there has been no known optical/IR counterpart for the object, no precise astrometric solution that correlates X-ray, radio, and optical positions and thus restricts the number of possible candidates, nor even published IR images of the field. We solve a previous radio/X-ray positional discrepancy, presenting the results of precise Chandra X-ray imaging, which definitively show that the radio source is positionally aligned with MXB 1730-335. At the same time, we have detected three additional low-luminosity (LX ~ 1034 ergs s-1) X-ray sources within two core radii, which are possibly quiescent low-mass X-ray binaries. We present both ground-based and Hubble Space Telescope (HST) infrared imaging of the field (in quiescent and bursting X-ray states of the RB), together with the necessary astrometric solution to overlay the radio/X-ray source positions. Even at HST resolution, the RB field is very complex and there are multiple candidates. No object of unusual color or of substantial variability in quiescent versus active or burst versus nonburst states is identified. Further, more sensitive HST NICMOS and/or ground-based, adaptive optics observations are needed to confidently identify the proper counterpart. In the case of the RB, uncertain but plausible calculations on the effects of the burst on the binary companion indicate that detection of a variable candidate should be feasible.

We discuss measurements of the properties of about 10,000 asteroids detected in 500 deg2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data. The moving objects are detected in the magnitude range 14 < r < 21.5, with a baseline of 5 minutes. Extensive tests show that the sample is at least 98% complete, with the contamination rate of less than 3%. We find that the size distribution of asteroids resembles a broken power-law, independent of the heliocentric distance: D^{-2.3} for 0.4 km 1 km in the asteroid belt, or about four times less than previous estimates. The distribution of main belt asteroids in the 4-dimensional SDSS color space is bimodal, and the two groups can be associated with S (rocky) and C (carbonaceous) asteroids. A strong bimodality is also seen in the heliocentric distribution of asteroids and suggests the existence of two distinct belts: the inner rocky belt, about 1 AU wide (FWHM) and centered at R~2.8 AU, and the outer carbonaceous belt, about 0.5 AU wide and centered at R~3.2 AU. The colors of Hungarias, Mars crossers, and near-Earth objects are more similar to the C-type than to S-type asteroids, suggesting that they originate in the outer belt. (abridged).

Early data taken during commissioning of the SDSS have resulted in the discovery of a very cool white dwarf. It appears to have stronger collision induced absorption from molecular hydrogen than any other known white dwarf, suggesting it has a cooler temperature than any other. While its distance is presently unknown, it has a surprisingly small proper motion, making it unlikely to be a halo star. An analysis of white dwarf cooling times suggests that this object may be a low-mass star with a helium core. The SDSS imaging and spectroscopy also recovered LHS 3250, the coolest previously known white dwarf, indicating that the SDSS will be an effective tool for identifying these extreme objects., 15 pages, including 5 figures. Accepted for Astrophysical Journal Letters

We present new astrometric solutions and infrared Hubble Space Telescope observations of GX 17+2 (X1813-140), one of the brightest X-ray sources on the celestial sphere. Despite 30 years of intensive study, and the existence of a strong radio counterpart with a sub-arcsecond position, the object remains optically unidentified. The observed X-ray characteristics strongly suggest that it is a so-called "Z-source," the rare but important category that includes Sco X-1 and Cyg X-2. Use of the USNO-A2.0 catalog enables us to measure the position of optical and infrared objects near the radio source to sub-arcsecond precision within the International Celestial Reference Frame, for direct comparison with the radio position, which we also recompute using modern calibrators. With high confidence we eliminate the V~17.5 star NP Ser, often listed as the probable optical counterpart of the X-ray source, as a candidate. Our HST NICMOS observations show two faint objects within our 0.5" radius 90% confidence error circle. Even the brighter of the two, Star A, is far fainter than expected (H~19.8), given multiple estimates of the extinction in this field and our previous understanding of Z sources, but it becomes the best candidate for the counterpart of GX 17+2. The probability of a chance coincidence of an unrelated faint object on the radio position is high. However, if the true counterpart is not Star A, it is fainter still, and our conclusion that the optical counterpart is surprisingly underluminous is but strengthened., 15 pages including 3 figures and 3 tables. Accepted for publication in The Astrophysical Journal

Four high-latitude slow variable stars have been noted by Meinunger (1972) as "nicht rote" ("not red") objects and thus curious. We have previously reported (Margon & Deutsch 1997) that one of these objects, CC Boo, is in fact a QSO. Here we present observations demonstrating that the remaining three are also highly variable active galactic nuclei. The most interesting object of the four is perhaps S 10765 (= NGP9 F324-0276706), which proves to be a resolved galaxy at z=0.063. Despite the rapid and large reported variability amplitude (~1.6 mag), the spectrum is that of a perfectly normal galaxy, with no emission lines or evident nonthermal continuum. We also present new spectroscopic and photometric observations for AR CVn, suggested by Meinunger to be an RR Lyrae star despite its very faint magnitude (=19.4). The object is indeed one of the most distant RR Lyrae stars known, at a galactocentric distance of ~40 kpc., Accepted for publication in Publications of the Astronomical Society of the Pacific, Volume 111, January 1999; 14 pages including 4 figures and 1 table

We have used innovative features of the Taurus Tunable Filter instrument on the 3.9-m Anglo-Australian Telescope to obtain nearly-continuous, high-throughput, linear photometry of V2116 Oph in a 7 Angstrom bandpass at the center of the O I 8446 emission line. This instrumental technique shows promise for applications requiring precise, rapid, narrowband photometry of faint objects. The spectrum of V2116 Oph, the counterpart of GX 1+4 (=X1728-247), is exotic, even among the unusual spectra of other optical counterparts of compact Galactic X-ray sources. The second strongest emission line is an unusual one, namely extremely prominent O I 8446, which is likely to result from pumping by an intense Ly beta radiation field. As the X-radiation from GX 1+4 is steadily pulsed, with typical pulsed fractions of 0.4, the O I 8446 emission in V2116 Oph may also be strongly modulated with the current 127 s period of the X-ray source. If so, this may well allow us to obtain high signal-to-noise radial velocity measurements and thus to determine the system parameters. However, no such pulsations are detected, and we set an upper limit of ~1% (full-amplitude) on periodic 8446 oscillations at the X-ray frequency. This value is comparable to the amplitude of continuum oscillations observed on some nights by other workers. Thus we rule out an enhancement of the pulsation amplitude in O I emission, at least at the time of our observations., 9 pages including 4 figures and no tables. Accepted for publication in PASP; to appear in Volume 110, August 1998

Using the Faint Object Spectrograph (FOS) aboard the Hubble Space Telescope, we have obtained the first time-resolved spectra of the King et al. ultraviolet-bright counterpart to the 11-minute binary X-ray source in the core of the globular cluster NGC 6624. This object cannot be readily observed in the visible, even from HST, due to a much brighter star superposed, Comment: 10 pages including 2 figures in Latex (AASTeX 4.0). Accepted for publication in vol. 482 (1997 June 10 issue) of The Astrophysical Journal (Letters)

We report high spatial resolution HST imagery and photometry of three well-studied, intense galactic X-ray binaries, X2129+47, CAL 87 and GX17+2. All three sources exhibit important anomalies, not readily interpreted by conventional models. Each source also lies in a severely crowded field, and in all cases the anomalies would be removed if much of the light observed from the ground in fact came from a nearby, thus-far-unresolved superposed companion. For V1727 Cyg (X2129+470), we find no such companion. We also present an HST FOS spectrum and broadband photometry which is consistent with a single, normal star. The supersoft LMC X-ray source CAL 87 was already known from ground-based work to have a companion separated by 0.9'' from the optical counterpart; our HST images clearly resolve these objects, and yield the discovery of an even closer, somewhat fainter additional companion. Our photometry indicates that contamination is not severe outside eclipse, where the companions only contribute 20% of the light in V, but during eclipse more than half of the V light comes from the companions. The previously-determined spectral type of the CAL 87 secondary may need to be reevaluated due to this significant contamination, with consequences on inferences of the mass of the components. We find no companions to NP Ser (=X1813-14, =GX17+2). However, for this object we point out a small but possibly significant astrometric discrepancy between the position of the optical object and that of the radio source which is the basis for the identification. This discrepancy needs to be clarified.

We report on follow-up observations of candidate X-ray bright, radio-quiet isolated neutron stars (INSs) identified from correlations of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) Data Release 4 in Ag\"ueros et al. (2006). We obtained Chandra X-ray Telescope exposures for 13 candidates in order to pinpoint the source of X-ray emission in optically blank RASS error circles. These observations eliminated 12 targets as good INS candidates. We discuss subsequent observations of the remaining candidate with the XMM-Newton X-ray Observatory, the Gemini North Observatory, and the Apache Point Observatory. We identify this object as a likely extragalactic source with an unusually high log(fX/fopt) ~ 2.4. We also use an updated version of the population synthesis models of Popov et al. (2010) to estimate the number of RASS-detected INSs in the SDSS Data Release 7 footprint. We find that these models predict ~3-4 INSs in the 11,000 square deg imaged by SDSS, which is consistent with the number of known INSs that fall within the survey footprint. In addition, our analysis of the four new INS candidates identified by Turner et al. (2010) in the SDSS footprint implies that they are unlikely to be confirmed as INSs; together, these results suggest that new INSs are not likely to be found from further correlations of the RASS and SDSS., Comment: 11 pages, 2 figures, 3 tables; accepted for publication in AJ

We have performed a comprehensive infrared imaging survey of 29 radio sources which were first detected by the UBC radio patrol survey of the galactic plane. The sources in our sample are the subset of variable and non-variable «control» objects which were mapped with the VLA by Duric & Gregory. Since other sources in the original variability survey have been shown to be associated with unusual galactic X-ray and gamma-ray sources, the aim of the present work was to make the first steps towards discovering whether the remaining radio variables represent a hitherto undetected sample of faint, unusual X-ray binary stars

We have obtained exposures of the field of X0512-401 in the globular cluster NGC1851, in X-rays with the Chandra X-ray Observatory, and in the far-UV with the Hubble Space Telescope. We derive an accurate new X-ray position within ~1" for X0512-401, which enables us to confirm that the only plausible candidate for the optical/UV counterpart is the Star A, which we previously identified from WFPC2 imaging. We find no evidence for X-ray or UV flux modulation on the ultra-short (, 5 pages, 2 figures, accepted for publication in ApJ Letters

The SEGUE survey obtained 240,000 moderate resolution (R = 1800) spectra from 3900 - 9000 Angstroms of fainter Milky Way stars (14.0 < g < 20.3) of a wide variety of spectral types, both main sequence and evolved objects, with the goal of studying the kinematics and populations of our Galaxy and its halo. The spectra are clustered in 212 regions spaced over three-quarters of the sky. Radial velocity accuracies for stars are 4 km/s at g < 18, degrading to 15 km/s at g = 20. For stars with S/N > 10 per resolution element, stellar atmospheric parameters are estimated, including metallicity, surface gravity, and effective temperature. SEGUE obtained 3500 square degrees of additional ugriz imaging (primarily at low Galactic latitudes) providing precise multi-color photometry (g,r,i = 2%), (u,z = 3%) and astrometry (0.1 arcsec) for spectroscopic target selection. The stellar spectra, imaging data, and derived parameter catalogs for this survey are publicly available as part of SDSS Data Release 7 (DR7)., 17 figures, AJ in press, updated to match Journal version

The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. While X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. We use optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709 stellar X-ray emitters cataloged in the RASS and falling within the SDSS Data Release 1 footprint. Most of these are bright stars with coronal X-ray emission unsuitable for SDSS spectroscopy, which is designed for fainter objects (g > 15 mag). Instead, we use SDSS photometry, correlations with the Two Micron All Sky Survey and other catalogs, and spectroscopy from the Apache Point Observatory 3.5 m telescope to identify these stellar X-ray counterparts. Our sample of 707 X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected samples of such stars. We derive distances to these stars using photometric parallax relations appropriate for dwarfs on the main sequence, and use these distances to calculate LX. We also identify a previously unknown cataclysmic variable (CV) as a RASS counterpart. Separately, we use correlations of the RASS and the SDSS spectroscopic catalogs of CVs and white dwarfs (WDs) to study the properties of these rarer X-ray-emitting stars. We examine the relationship between (fX/fg) and the equivalent width of the Hbeta emission line for 46 X-ray-emitting CVs and discuss tentative classifications for a subset based on these quantities. We identify 17 new X-ray-emitting DA (hydrogen) WDs, of which three are newly identified WDs. (abridged), 23 pages, 15 figures, 8 tables; full catalog available online only

With the Sixth Data Release of the Sloan Digital Sky Survey, the imaging of the Northern Galactic Cap is now complete. The survey contains images and parameters of roughly 287 million objects over 9583 deg^2, and 1.27 million spectra of stars, galaxies, quasars and blank sky (for sky subtraction) selected over 7425 deg^2. This release includes much more extensive stellar spectroscopy than previously, and also includes detailed estimates of stellar temperatures, gravities, and metallicities. The results of improved photometric calibration are now available, with uncertainties of roughly 1% in g, r, i, and z, and 2% in u, substantially better than the uncertainties in previous data releases. The spectra in this data release have improved wavelength and flux calibration, especially in the extreme blue and extreme red, leading to the qualitatively better determination of stellar types and radial velocities. The spectrophotometric fluxes are now tied to point spread function magnitudes of stars rather than fiber magnitudes, giving a 0.35 mag change in the spectrophotometric flux scale. Systematic errors in the velocity dispersions of galaxies have been fixed, and the results of two independent codes for determining spectral classifications and redshifts are made available. (Abridged), 21 pages with 8 color figures. ApJS, in press. Minor modifications from previous version

This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and represents the completion of the SDSS-I project (whose successor, SDSS-II will continue through mid-2008). It includes five-band photometric data for 217 million objects selected over 8000 square degrees, and 1,048,960 spectra of galaxies, quasars, and stars selected from 5713 square degrees of that imaging data. These numbers represent a roughly 20% increment over those of the Fourth Data Release; all the data from previous data releases are included in the present release. In addition to "standard" SDSS observations, DR5 includes repeat scans of the southern equatorial stripe, imaging scans across M31 and the core of the Perseus cluster of galaxies, and the first spectroscopic data from SEGUE, a survey to explore the kinematics and chemical evolution of the Galaxy. The catalog database incorporates several new features, including photometric redshifts of galaxies, tables of matched objects in overlap regions of the imaging survey, and tools that allow precise computations of survey geometry for statistical investigations., Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS Sixth Data Release (DR6) is now public, available from http://www.sdss.org

We present spatially-resolved, moderate-resolution spectrophotometry of the recurrent nova T Pyx and a portion of the surrounding shell. The spectrum extracted from a strip of width 10'' centered on the star shows well-known, strong emission lines typical of old novae, plus a prominent, unfamiliar emission line at 6590 Angstroms. This line, and a weaker companion at 6540 Angstroms which we also detect, have been previously reported by Shahbaz et al., and attributed to Doppler-shifted H alpha emission from a collimated jet emerging from T Pyx. We demonstrate that these lines are instead due to [NII] 6548, 6584 from a complex velocity field in the surrounding nebula. The comments of past workers concerning the great strength of HeII 4686 in T Pyx itself are also reiterated., Comment: 8 pages including 2 figures; Accepted for publication in The Astrophysical Journal Letters

We report on the Chandra X-ray Observatory observations of the globular cluster NGC 288. We detect four X-ray sources within the core radius and seven additional sources within the half-mass radius down to a limiting luminosity of Lx=7e30 erg/s (assuming cluster membership) in the 0.3-7 keV band. We also observed the cluster with the Hubble Space Telescope Advanced Camera for Surveys and identify optical counterparts to seven X-ray sources out of the nine sources within the HST field-of-view. Based on the X-ray and optical properties, we find 2-5 candidates of cataclysmic variables (CVs) or chromospherically active binaries, and 2-5 background galaxies inside the half-mass radius. Since the core density of NGC 288 is very low, the faint X-ray sources of NGC 288 found in the Chandra and HST observations is higher than the prediction on the basis of the collision frequency. We suggest that the CVs and chromospherically active binaries are primordial in origin, in agreement with theoretical expectation., Comment: 11 pages, 6 figures; accepted for publication in ApJ

This paper describes the fourth data release of the Sloan Digital Sky Survey (SDSS), including all survey-quality data taken through June 2004. The data release includes five-band photometric data for 180 million objects selected over 6670 deg^2, and 673,280 spectra of galaxies, quasars, and stars selected from 4783 deg^2 of that imaging data using the standard SDSS target selection algorithms. These numbers represent a roughly 25% increment over those of the Third Data Release. The Fourth Data Release also includes an additional 131,840 spectra of objects selected using a variety of alternative algorithms, to address scientific issues ranging from the kinematics of stars in the Milky Way thick disk to populations of faint galaxies and quasars., Comment: 26 pages, 2 figures

Only seven radio-quiet isolated neutron stars (INSs) emitting thermal X rays are known, a sample that has yet to definitively address such fundamental issues as the equation of state of degenerate neutron matter. We describe a selection algorithm based on a cross-correlation of the ROSAT All-Sky Survey (RASS) and the Sloan Digital Sky Survey (SDSS) that identifies X-ray error circles devoid of plausible optical counterparts to the SDSS g~22 magnitudes limit. We quantitatively characterize these error circles as optically blank; they may host INSs or other similarly exotic X-ray sources such as radio-quiet BL Lacs, obscured AGN, etc. Our search is an order of magnitude more selective than previous searches for optically blank RASS error circles, and excludes the 99.9% of error circles that contain more common X-ray-emitting subclasses. We find 11 candidates, nine of which are new. While our search is designed to find the best INS candidates and not to produce a complete list of INSs in the RASS, it is reassuring that our number of candidates is consistent with predictions from INS population models. Further X-ray observations will obtain pinpoint positions and determine whether these sources are entirely optically blank at g~22, supporting the presence of likely isolated neutron stars and perhaps enabling detailed follow-up studies of neutron star physics., Accepted for publication in the AJ; higher resolution figures available at http://www.astro.washington.edu/agueros/pub/

Discoveries of two new white dwarf plus M star binaries with striking optical cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to six the total number of X-ray faint, magnetic accretion binaries that accrete at rates < 10^{-13} Msun/yr, or 3 hr. Optical surveys for the cyclotron harmonics appear to be the only means of discovery, so the space density of pre-Polars could rival that of Polars, and the binaries provide an important channel of progenitors (in addition to the asynchronous Intermediate Polars). Both physical and SDSS observational selection effects are identified that may help to explain the clumping of all six systems in a narrow range of magnetic field strength around 60 MG., 25 pages, 13 figures, Accepted to ApJ

We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72 h^{-3} Gpc^3 over 3816 square degrees and 0.16, Comment: Submitted to the ApJ. Additional pedagogical material and numerical data at http://cmb.as.arizona.edu/~eisenste/acousticpeak