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We present far- and near-ultraviolet absorption spectroscopy of the $\sim$23 Myr edge-on debris disk surrounding the A0V star $\eta$ Telescopii, obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. We detect absorption lines from C I, C II, O I, Mg II, Al II, Si II, S II, Mn II, Fe II, and marginally N I. The lines show two clear absorption components at $-22.7\pm0.5$ km s$^{-1}$ and $-17.8\pm0.7$ km s$^{-1}$, which we attribute to circumstellar (CS) and interstellar (IS) gas, respectively. CO absorption is not detected, and we find no evidence for star-grazing exocomets. The CS absorption components are blueshifted by $-16.9\pm2.6$ km s$^{-1}$ in the star's reference frame, indicating that they are outflowing in a radiatively driven disk wind. We find that the C/Fe ratio in the $\eta$ Tel CS gas is significantly higher than the solar ratio, as is the case in the $\beta$ Pic and 49 Cet debris disks. Unlike those disks, however, the measured C/O ratio in the $\eta$ Tel CS gas is consistent with the solar value. Our analysis shows that because $\eta$ Tel is an earlier type star than $\beta$ Pic and 49 Cet, with more substantial radiation pressure at the dominant C II transitions, this species cannot bind the CS gas disk to the star as it does for $\beta$ Pic and 49 Cet, resulting in the disk wind., Comment: Accepted to AJ; 24 pages, 18 figures

Gas has been detected in a number of debris disks. It is likely secondary, i.e. produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk around the 15--30 Myr old A-type star HD 32297. We find that C$^0$ is located in a ring at $\sim$110 au with a FWHM of $\sim$80 au, and has a mass of $(3.5\pm0.2)\times10^{-3}$ M$_\oplus$. Naively, such a surprisingly small mass can be accumulated from CO photo-dissociation in a time as short as $\sim$10$^4$ yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C$^0$ and CO observations, is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of $\sim$15 M$_\oplus$ Myr$^{-1}$, much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and re-release. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks., accepted for publication in the ApJ

Kiefer et al. reported the detection of infalling Ca II absorption in HD 172555, a member of the beta Pictoris Moving Group (beta PMG). We obtained HST Space Telescope Imaging Spectrograph and Cosmic Origins Spectrograph spectroscopy of this star at 2 epochs separated by a week, and we report the discovery of infalling gas in resonant transitions of Si III and IV, C II and IV, and neutral atomic oxygen. Variable absorption is seen in the C II transitions and is optically thick, with covering factors which range between 58% and 68%, similar to features seen in beta Pictoris. The O I spectral profile resembles that of C II, showing a strong low-velocity absorption to + 50 km s(-1) in the single spectral segment obtained during orbital night, as well as what may be higher-velocity absorption. Studies of the mid-IR spectrum of this system have suggested the presence of silica. The O I absorption differs from that seen in Si III, suggesting that the neutral atomic oxygen does not originate in SiO dissociation products but in a more volatile parent molecule such as CO.

We present medium resolution ultraviolet absorption measurements recorded with the HST-COS and FUSE spectrographs towards the Wolf-Rayet star UIT-236 belonging to the BCLMP 99 HII region in the M33 galaxy. We have detected at least 5 major absorption systems along the 840 kpc sight-line to UIT-236 with average gas cloud LSR velocities of � 205, � 170, � 135, � 32, and þ3 kms � 1 . The three most negative velocity cloud components, which we associate with gas in the M33 galaxy, have been detected in the line profiles of CII, CII � ,CIII, NI, NII, OI, OVI, SiII, SiII � , SiIII, SiIV, PII, SII, ArI, FeII, and FeIII ions. These profiles have been fit with absorption models to determine ion column densities for each cloud component. For the case of highly ionized gas components, the observed column density ratios of OVI/SiIVare most compatible with the predictions of ionization by turbulent mixing layers or in a shock driven medium. A possible formation scenario is that the SiIV is formed within a photo-ionized stellar wind bubble that is being driven into surrounding gas that collisionally produces the observed OVI ions. Using the column density ratios of the CII=CIIlines, we have determined electron density values in the range 1:8-6:0 cm � 3 for the ionized M33 gas clouds. Such values are similar to those found for other ionized interstellar bubbles such as N51D (in the Large Magellanic Cloud), γ 2 Vel, and NGC 2244 (the Rosette Nebula). We have carried out a gas phase element abundance analysis of the three cloud components, indicating that C, N, O, Si, P, Ar, Fe, and Ni are all depleted relative to their solar abundancevalues. This pattern is confirmed by the observed N(OI)/N(HI) column density ratios which suggest a low metallicity for all three of the neutral gas com- ponents. The presence of interstellar shocks and expanding supershells of gas driven by stellar wind outflows from stars like UIT-236 may well account for the element depletion values observed along the M33 sight-line.

We present medium spectral resolution (R ~ 60,000) observations of the CaII K-line (3,933 A) absorption profiles observed toward 21 nearby A-type stars thought to possess circumstellar gas debris disks. The stars were repeatedly observed over two observing runs on the 2.1 m Otto Struve telescope at the McDonald Observatory, Texas in 2011 May and 2012 November. Nightly changes in the absorption strength of the CaII K-line near the stellar radial velocity were observed in four of the stars (HD 21620, HD 110411, HD 145964 and HD 183324). This type of absorption variability indicates the presence of a circumstellar gas disk around these stars. We also have detected weak absorption features that sporadically appear with velocities in the range ± 100 km s-1 of the main circumstellar K-line in the spectra of HD 21620, HD 42111, HD 110411 and HD 145964. Due to the known presence of both gas and dust disks surrounding these four stars, these transient absorption features are most probably associated with the presence of Falling Evaporated Bodies (FEBs, or exocomets) that are thought to liberate gas on their grazing trajectory toward and around the central star. This now brings the total number of A-type stars in which the evaporation of CaII gas from protoplanetary bodies (i.e., exocomets) has been observed to vary on a nightly basis to 10 systems. A statistical analysis of the 10 A-stars showing FEB-activity near the CaII K-line compared to 21 A-type stars that exhibit no measurable variability reveals that FEB-activity occurs in significantly younger stellar systems that also exhibit chemical peculiarities. The presence of FEB-activity does not appear to be associated with a strong mid-IR excess. This is probably linked to the disk inclination angle, since unless the viewing angle is favorable the detection of time-variable absorption may be unlikely. Additionally, if the systems are more evolved then the evaporation of gas due to FEB activity could have ceased, whereas the circumstellar dust disk may still remain.

We present estimates of the contribution from 33 nearby (d

We present medium resolution ultraviolet absorption measurements recorded with the HST-COS and FUSE spectrographs towards two post-AGB stars (UIT-1 and B1754) associated with the NGC 6752 globular cluster. We have detected intermediate velocity (IV) gas with Vlsr ~ +38 km s-1 along the 3.9 kpc sight-line to the cluster in the absorption profiles of the CII, CII*, CIV, NI, OI, OVI, AlII, SiII, SiIV, SII, FeII and FeIII ions. The distance to this "multi-phase" IV gas lies in the 0.56-3.9 kpc range. We have fit the IV absorption profiles with models to determine column density values for the various ions. For the case of the highly ionized IV components the column density ratios of the SiIV, CIV, NV and OVI lines are most compatible with the predictions of ionization by turbulent mixing layers, shocks or halo SNRs. A gas-phase abundance analysis of the IV gas indicates that C, N, O, Al, Si and Fe appear to possess sub-solar metallicity values relative to that of sulfur. However, when the effects of element depletion onto interstellar dust in the halo is accounted for, the IVC gas probably has a value near to (or slightly less than) solar metallicity. The IV gas that is streaming away from the Galaxy is located within 3.9 kpc and its origin may well be linked to a galactic fountain in the disk. The IVC may be part of the trailing edge of the WE HVC complex, whose many constituent small clouds also possess positive velocities in this galactic direction.

We present medium resolution (R = 60,000) absorption measurements of the interstellar Ca II K line observed towards five nearby A-type stars (49 Ceti, 5 Vul, ι Cyg, 2 And, and HD 223884) suspected of possessing circumstellar gas debris disks. The stars were observed on a nightly basis during a six night observing run on the 2.1-meter Otto Struve telescope at the McDonald Observatory, Texas. We have detected nightly changes in the absorption strength of the Ca II K line observed near the stellar radial velocity in three of the stars (49 Ceti, i Cyg and HD 223884). Such changes in absorption suggest the presence of a circumstellar (atomic) gas disk around these stars. In addition to the absorption changes in the main Ca II K line profile, we have also observed weak transient absorption features that randomly appear at redshifted velocities in the spectra of 49 Ceti, 5 Vul, and 2 And. These absorption features are most probably associated with the presence of falling evaporated bodies (exo-comets) that liberate evaporating gas on their approach to the central star. This now brings the total number of systems in which exocomet activity has been observed at Ca II or Na I wavelengths on a nightly basis to seven (β Pic, HR 10, HD 85905, β Car, 49 Ceti, 5 Vul, and 2 And), with 2 And exhibiting weaker and less frequent changes. All of the disk systems presently known to exhibit either type of short-term variability in Ca II K line absorption are rapidly rotating A-type stars (V sin i > 120 km s-1). Most exhibit mid-IR excesses, and many of them are very young (< 20 Myr), thus supporting the argument that many of them are transitional objects between Herbig Ae and "Vega-like" A-type stars with more tenuous circumstellar disks. No mid-IR excess (due to the presence of a dust disk) has yet been detected around either 2 And or HD 223884, both of which have been classified as λ Bootis-type stars. This may indicate that the observed changes in gas absorption for these two stars may not be due to circumstellar activity, but may instead be associated with the stars' episodic mass loss and passage though low-density interstellar clouds.

We present well-sampled ultraviolet (UV) light curves of seven RR Lyrae stars (SW Aqr, HL Her, SDSS J100133.3 + 014328.1, SDSS J104844.1 + 581539.4, SDSS J105513.7 + 564747.0, SDSS J105622.2 + 570520.6, and USNO-B1.0 1024-0010686) serendipitously obtained with the NASA GALEX satellite that show changes of up to AB=6.5 mag in the far-ultraviolet (FUV; 1350-1800 A) wavelength band. For the test case SW Aqr, we combine the GALEX FUV and NUV (1800-2800 A) observations with visible U, B, and V photometry to determine the variation of physical parameters such as temperature, surface gravity, and radius during the RR Lyrae pulsation cycle of 0.459299 days. Assuming that SW Aqr changes temperature from 6100 K to 8400 K over this cycle, we find that the FUV and NUV light curves can be well matched using the 2004 stellar atmosphere models of Castelli and Kurucz (CK) and a best-fit metallicity of [Fe/H] = -1.5. Pulsation periods are also found for the remaining six stars from their UV light curves, and we have shown that the UV data are consistent with the predictions of CK models using an assumed temperature variation of 6100 K to 8000 K and a log g variation of 2.15 to 3.75 over the pulsation cycle for assumed metallicity values of -2.0 < [Fe/H] < 0.0. Our main finding from the present analysis is that CK models can be successfully used to predict the light-curve behavior of RR Lyrae stars at UV wavelengths if the minimum and maximum temperatures are known from (preferably) visible light-curve observations, such that the stellar metallicity values can be derived. Finally, we note that the model fits to the GALEX data are quite sensitive to the light curves around minimum light, such that the best-fit metallicity is well constrained over this region of the pulsation cycle.

We have analysed a sample of 23 hot DAs to better understand the source of the circumstellar features reported in previous work. Unambiguous detections of circumstellar material are again made at eight stars. The velocities of the circumstellar material at three of the white dwarfs are coincident with the radial velocities of interstellar medium (ISM) along the sightline to the stars, suggesting that the objects may be ionizing the ISM in their locality. In three further cases, the circumstellar velocities are close to the ISM velocities, indicating that these objects are ionizing either the ISM or evaporated planetesimals/material in a circumstellar disc. The circumstellar velocity at WD 1614−084 lies far from the ISM velocities, indicating the ionization of either an undetected ISM component or circumstellar material. The material seen at WD 0232+035 can be attributed to the photoionization of material lost from its M dwarf companion. The measured column densities of the circumstellar material lie within the

The Berkeley Visible Imaging Tube (BVIT) was installed on the Southern African Large Telescope (SALT) in January 2009 and subsequently refurbished in August 2010. BVIT is an imaging, photon counting camera with multi-color (B, V, R, and H-α) capability. At the heart of BVIT is a 25 mm diameter active area, microchannel plate, sealed tube device with a visible photocathode and a cross-delay line readout. For each detected event the readout electronics record an X, Y position, an event pulse size (P), and an arrival time (T) — recorded with 25 ns precision. Post-acquisition processing of the X, Y, P, and T photon lists can be used to build images and light curves (to whatever sampling rate is supported by the signal to noise of the source as detected). The instrument design is presented as well as some examples of data acquired with the instrument on SALT.

We present a brief description of the Berkeley Visible Imaging Tube (BVIT) detector system, which is a user instrument on the 10-m Southern African Large Telescope (SALT), and include some preliminary observational results gained in mid-2011. The data show that BVIT is capable of revealing emission features occurring on time-scales of < 0.1 sec, thus opening up for the general user a window of high time-resolution astronomy at visible wavelengths.

We present new high-speed, multi-observatory, multi-instrument photometry of the eclipsing polar UZ For in order to measure precise mid-eclipse times with the aim of detecting any orbital period variations. When combined with published eclipse times and archival data spanning ~27 years, we detect departures from a linear and quadratic trend of ~60 s. The departures are strongly suggestive of two cyclic variations of 16(3) and 5.25(25) years. The two favoured mechanisms to drive the periodicities are either two giant extrasolar planets as companions to the binary (with minimum masses of 6.3(1.5)M(Jupiter) and 7.7(1.2)M(Jupiter)) or a magnetic cycle mechanism (e.g. Applegate's mechanism) of the secondary star. Applegate's mechanism would require the entire radiant energy output of the secondary and would therefore seem to be the least likely of the two, barring any further refinements in the effect of magnetic fieilds (e.g. those of Lanza et al.). The two planet model can provide realistic solutions but it does not quite capture all of the eclipse times measurements. A highly eccentric orbit for the outer planet would fit the data nicely, but we find that such a solution would be unstable. It is also possible that the periodicities are driven by some combination of both mechanisms. Further observations of this system are encouraged.

We present medium-resolution ultraviolet interstellar absorption measurements recorded with the HST-COS and FUSE spectrographs toward the post-AGB star Barnard 29 in the M13 globular cluster. Inspection of the UV spectra has revealed absorption at VLSR~-60 km s-1 in the absorption profiles of the C I, C II, C II*, C IV, N I, N II, N V, O I, ALII, Si II, Si IV, S II and Fe II ions. This component can be associated with an intermediate-velocity cloud (IVC), previously identified by both radio and visible observations. More importantly, these data have newly revealed high-velocity absorption at VLSR = -121 ± 3 km s-1 in the UV ions of C II, C III, C IV, N II, Si II, and Si IV. This absorption is thought to arise in a highly ionized, multiphase high-velocity cloud (HVC) located a distance of 0.46 +0.40 ± 0.21 and [C/N] = +0.10 ± 0.25 for the HVC gas component. These values indicate that the H V gas has higher than solar relative abundances, consistent with gas of a supersolar metallicity. Several other highly ionized HVCs with distances of less than 7.5 kpc have recently been shown to possess similarly high-metallicity values that are consistent with an origin in condensing returning gas from a galactic fountain.

We measure the UV-optical color dependence of galaxy clustering in the local universe. Using the clean separation of the red and blue sequences made possible by the NUV - r color-magnitude diagram, we segregate the galaxies into red, blue and intermediate "green" classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies shows strong redshift space distortion on small scales -- the "finger-of-God" effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, \xi (r_p, \pi) for all three samples show the effect of large-scale streaming from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected auto-correlation function w_p(r_p) for red and green galaxies fits a power-law with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma ~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the clustering of a fiducial L* galaxy, the red, green, and blue have a relative bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display an increase in convexity at ~ 1 Mpc/h, with an excess of large scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive halos, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and color.

We present GALEX near ultraviolet (NUV:1750 - 2750A) and far ultraviolet (FUV: 1350 - 1750A) imaging observations of two 1.2 degree diameter fields in the Hyades and Pleiades open clusters in order to detect possible UV variability of the member stars. We have performed a detailed software search for short-term UV flux variability during these observations of the approx 400 sources detected in each of the Hyades and Pleiades fields to identify flare-like (dMe) stellar objects. This search resulted in the detection of 16 UV variable sources, of which 13 can be directly associated with probable M-type stars. The other UV sources are G-type stars and one newly discovered RR Lyrae star, USNOB1.0 1069-0046050, of period 0.624 day and distance 4.5-7.0 kpc. Light curves of photon flux versus time are shown for 7 flare events recorded on six probable dMe stars. UV energies for these flares span the range 2E27 to 5E29 erg, with a corresponding NUV variability change of 1.82 mag. Only one of these flare events (on the star Cl* Melotte 25 LH129) can definitely be associated with an origin on a member the Hyades cluster itself. Finally, many of our M-type candidates show long periods of enhanced UV activity but without the associated rapid increase in flux that is normally associated with a flare event. However, the total UV energy output during such periods of increased activity is greater than that of many short-term UV flares. These intervals of enhanced low-level UV activity concur with the idea that, even in quiescence, the UV emission from dMe stars may be related to a superposition of many small flare events possessing a wide range of energies., Comment: PASP Submitted

We present a detailed study of the Galaxy Evolution Explorer's photometric catalogs with special focus on the statistical properties of the All-sky and Medium Imaging Surveys. We introduce the concept of primaries to resolve the issue of multiple detections and follow a geometric approach to define clean catalogs with well-understood selection functions. We cross-identify the GALEX sources (GR2+3) with Sloan Digital Sky Survey (DR6) observations, which indirectly provides an invaluable insight about the astrometric model of the UV sources and allows us to revise the band merging strategy. We derive the formal description of the GALEX footprints as well as their intersections with the SDSS coverage along with analytic calculations of their areal coverage. The crossmatch catalogs are made available for the public. We conclude by illustrating the implementation of typical selection criteria in SQL for catalog subsets geared toward statistical analyses, e.g., correlation and luminosity function studies., Comment: 12 pages, 15 figures, accepted to ApJ

The GALEX (Galaxy Evolution Explorer) spectroscopic survey mode, with a resolution of about 8 A in the FUV (1350 - 1750 A) and about 20 A in the NUV (1950 - 2750 A) is used for a systematic search of Ly-a emitting galaxies at low redshift. This aims at filling a gap between high-redshift surveys and a small set of objects studied in detail in the nearby universe. A blind search of 7018 spectra extracted in 5 deep exposures (5.65 sq.deg) has resulted in 96 Ly-a emitting galaxy candidates in the FUV domain, after accounting for broad-line AGNs. The Ly-a EWs (equivalent width) are consistent with stellar population model predictions and show no trends as a function of UV color or UV luminosity, except a possible decrease in the most luminous that may be due to small-number statistics. Their distribution in EW is similar to that at z about 3 but their fraction among star-forming galaxies is smaller. Avoiding uncertain candidates, a sub-sample of 66 objects in the range 0.2 < z < 0.35 has been used to build a Ly-a LF (luminosity function). The incompleteness due to objects with significant Ly-a emission but a UV continuum too low for spectral extraction has been evaluated. A comparison with H-a LF in the same redshift domain is consistent with an average Ly-a/H-a of about 1 in about 15 % of the star-forming galaxies. A comparison with high-redshift Ly-a LFs implies an increase of the Ly-a luminosity density by a factor of about 16 from z about 0.3 to z about 3. By comparison with the factor 5 increase of the UV luminosity density in the same redshift range, this suggests an increase of the average Ly-a escape fraction with redshift.

I present a short review of the physical properties and relationships between warm partially ionized and hot and highly ionized gas in the local interstellar-medium (ISM). The majority of the measurements reviewed have been obtained through ultraviolet absorption spectroscopy recorded towards stellar targets located within ∼150 pc of the Sun. Many questions still remain to be answered concerning the location, temperature, density and source of ionization of both of these phases of the diffuse interstellar gas. In particular, we focus on absorption observations of the ions of C IV λ 1550 A and Si IV λ 1394 A and discuss if highly ionized gas (as traced by the O VI λ 1032 A ion) has in fact actually been detected within the Local Cavity.

We present the preliminary results from implementing a new software tool that enables inspection of time-tagged photon data for the astronomical sources contained within individual GALEX ultraviolet images of the sky. We have inspected the photon data contained within 1802 GALEX images to reveal rapid, short-term (, Accepted for the Astrophysical Journal Supplement, GALEX Special Issue

We describe the calibration status and data products pertaining to the GR2 and GR3 data releases of the Galaxy Evolution Explorer (GALEX). These releases have identical pipeline calibrations that are significantly improved over the GR1 data release. GALEX continues to survey the sky in the far-ultraviolet (FUV, ~154 nm) and near-ultraviolet (NUV, ~232 nm) bands, providing simultaneous imaging with a pair of photon-counting, microchannel plate, delay line readout detectors. These 1.25° field of view detectors are well suited to ultraviolet observations because of their excellent red rejection and negligible background. A dithered mode of observing and photon list output pose complex requirements on the data processing pipeline, entangling detector calibrations, and aspect reconstruction algorithms. Recent improvements have achieved photometric repeatability of 0.05 and 0.03 m_(AB) in the FUV and NUV, respectively. We have detected a long-term drift of order 1% FUV and 6% NUV over the mission. Astrometric precision is of order 0.5" rms in both bands. In this paper we provide the GALEX user with a broad overview of the calibration issues likely to be confronted in the current release. Improvements are likely as the GALEX mission continues into an extended phase with a healthy instrument, no consumables, and increased opportunities for guest investigations.

We use GALEX/optical photometry to construct color-color relationships for early-type galaxies sorted by morphological type. We have matched objects in the GALEX GR1 public release and the first IR1.1 internal release, with the RC3 early-type galaxies having a morphological type -5.5, Comment: 25 pages, 5 figures, accepted for publication in ApJS (abstract abridged), typos corrected in section 2.1

We present ultraviolet (UV) photometry of M31 globular clusters (GCs) found in 23 Galaxy Evolution Explorer (GALEX) images covering the entirety of M31. We detect 485 and 273 GCs (and GC candidates) in the near-ultraviolet (NUV; 2267 A) and far-ultraviolet (FUV; 1516 A), respectively. Comparing M31 data with those of Galactic GCs in the UV with the aid of population models, we find that the age ranges of old GCs in M31 and the Galactic halo are similar. Three metal-rich ([Fe/H]>-1) GCs in M31 produce significant FUV flux making their FUV-V colors unusually blue for their metallicities. These are thought to be analogs of the two peculiar Galactic GCs NGC 6388 and NGC 6441 with extended blue HB stars. Based on the models incorporating helium enriched subpopulations in addition to the majority of the population that have a normal helium abundance, we suggest that even small fraction of super-helium-rich subpopulations in GCs can reproduce the observed UV bright metal-rich GCs. Young clusters in M31 show distinct UV and optical properties from GCs in Milky Way. Population models indicate that their typical age is less than ~ 2 Gyrs. A large fraction of young GCs have the kinematics of the thin, rapidly rotating disk component. However, a subset of the old GCs also shares the thin-disk kinematics of the younger clusters. The existence of young GCs on the outskirts of M31 disk suggests the occurrence of a significant recent star formation in the thin-disk of M31. Old thin-disk GCs may set constraints on the epoch of early formation of the M31 thin-disk. We detect 12 (10) intermediate-age GC candidates in NUV (FUV). We suggest that some of spectroscopically identified intermediate-age GCs may not be truly intermediate in age, but rather older GCs that possess developed HB., 43 pages, 14 figures, accepted for the GALEX special issue of ApJS

We report on the properties of a sample of ultraviolet-luminous galaxies (UVLGs) selected by matching the Galaxy Evolution Explorer (GALEX) All-Sky Imaging and Medium Imaging Surveys with the Sloan Digital Sky Survey third data release. The overlap between these two surveys is roughly 450 deg^2. Of 25,362 galaxies (with SDSS spectroscopy) in the range 0.0 < z < 0.3 detected by GALEX, there are 215 galaxies with L > 2 × 10^(10) L_☉ at 1530 Å (observed wavelength). The properties of this population are well correlated with ultraviolet surface brightness. We find that the galaxies with low UV surface brightness are primarily large spiral systems with a mixture of old and young stellar populations, while the high surface brightness galaxies consist primarily of compact starburst systems, with an approximate boundary at a surface brightness of I_(1530) = 10^8 L_☉ kpc^(−2). The large galaxies appear to be the high-luminosity tail of the galaxy star formation function and owe their large luminosity to their large surface area. In terms of the behavior of surface brightness with luminosity, size with luminosity, the mass-metallicity relation, and other parameters, the compact UVLGs clearly depart from the trends established by the full sample of galaxies. The subset of compact UVLGs with the highest surface brightness (I_(1530) > 10^9 L_☉ kpc^(−2); "supercompact UVLGs") have characteristics that are remarkably similar to Lyman break galaxies at higher redshift. They are much more luminous (and thus have much higher star formation rates) than typical local ultraviolet-bright starburst galaxies and blue compact dwarf galaxies. They have metallicities that are systematically lower than normal galaxies of the same stellar mass, indicating that they are less chemically evolved. In all these respects, they are the best local analogs for Lyman break galaxies.

We present analysis of time-variable, shifted absorption features in far-UV spectra of the unusual 49 Ceti debris disk. This nearly edge-on disk is one of the brightest known, and is one of the very few containing detectable amounts of circumstellar gas as well as dust. In our two visits of Hubble Space Telescope STIS spectra, variable absorption features are seen on the wings of lines arising from C II and C IV, but not for any of the other circumstellar absorption lines. Similar variable features have long been seen in spectra of the well-studied $\beta$ Pictoris debris disk and attributed to the transits of star-grazing comets. We calculate the velocity ranges and apparent column densities of the 49 Cet variable gas, which appears to be moving at velocities of tens to hundreds of km s$^{-1}$ relative to the central star. The velocities of the gas in the redshifted variable event in Visit 2 show that the maximum distances of the infalling gas at the time of transit are about 0.05 to 0.2 AU from the central star. A preliminary attempt at a composition analysis of the redshifted event suggests that the C/O ratio in the infalling gas may be super-solar, as it is in the bulk of the stable disk gas., Comment: 6 pages, 7 figures accepted to ApJ, figure 7 updated to most recent version

Diffuse far-UV emission arising from the edge of the Orion-Eridanus superbubble was observed with the SPEAR imaging spectrometer, revealing numerous emission lines arising from both atomic species and H2. Spatial variations in line intensities of CIV, SiII, and OVI, in comparison with soft X-ray, H-alpha and dust data, indicate that these ions are associated with processes at the interface between hot gas inside the bubble and the cooler ambient medium. Thus our observations probe physical conditions of an evolved thermal interface in the ISM.

We present medium-resolution spectra (R ∼ 7.5 km s −1 ) of the interstellar NaI and CaII interstellar absorption lines observed towards 16 early-type stars with distances of 160-1 kpc in the line-of-sight towards the Orion-Eridanus Superbubble (OE-S). These data have been supplemented with measurements of NaI absorption towards a further 13 stars with similar sight-lines taken from the literature. We detect two major absorption components with velocities of Vlsr ∼ +7.0 and −8.0 km s −1 . The former component, seen in 70% of the sight-lines is associated with the boundary to the Local Bubble cavity located at a distance of 140-150 pc. The other absorption component is only detected towards a limited region of the sky bounded by (190 ◦ 220 pc within an area coincident with that of the 0.75 keV X-ray enhancement of the OE-S. Column density ratios, N(NaI)/N(CaII), for the most negative velocity components have values 500 pc. Finally, we place a similar distance limit for any coherently structured rear shell of neutral gas associated with expansion of the OE-S towards the galactic halo.

We present version 1.0 of the NASA Galaxy Evolution Explorer (GALEX) ultraviolet variability (GUVV) catalog, which contains information on 84 time-variable and transient sources gained with simultaneous near-ultraviolet (NUV) and far-ultraviolet (FUV) photometric observations. These time-variable sources were serendipitously revealed in the various 12 diameter star fields currently being surveyed by the GALEX satellite in two ultraviolet bands (NUV 1750–2750 A, FUV 1350–1750 A) with limiting AB magnitudes of 23–25. The largest amplitude variable objects currently detected by GALEX are M dwarf flare stars, which can brighten by 5–10 mag in both the NUV and FUV bands during short-duration (

We present the first Galaxy Evolution Explorer (GALEX) UV images of the well-known interacting group of galaxies, Stephan's Quintet (SQ). We detect widespread UV emission throughout the group. However, there is no consistent coincidence between UV structure and emission in the optical, Hα, or H I. Excluding the foreground galaxy NGC 7320 (Sd), most of the UV emission is found in regions associated with the two spiral members of the group, NGC 7319 and NGC 7318b, and the intragroup medium starburst SQ-A. The extinction-corrected UV data are analyzed to investigate the overall star formation activity in SQ. We find that the total star formation rate (SFR) of SQ is 6.69 ± 0.65 M☉ yr-1. Of this, 1.34 ± 0.16 M☉ yr-1 is due to SQ-A. This is in excellent agreement with that derived from the extinction-corrected Hα luminosity of SQ-A. The SFR in regions related to NGC 7319 is 1.98 ± 0.58 M☉ yr-1, most of which (68%) is contributed by the disk. The contribution from the young tail is only 15%. In the UV, the young tail is more extended (~100 kpc) and shows a looplike structure, including the optical tail, the extragalactic H II regions recently discovered in Hα, and other UV emission regions discovered for the first time. The UV and optical colors of the old tail are consistent with a single stellar population of age t 108.5±0.4 yr. The UV emission associated with NGC 7318b is found in a very large (~80 kpc) disk, with a net SFR of 3.37 ± 0.25 M☉ yr-1. Several large UV emission regions are 30-40 kpc away from the nucleus of NGC 7318b. Although both NGC 7319 and NGC 7318b show peculiar UV morphology, their SFR is consistent with that of normal Sbc galaxies, indicating that the strength of star formation activity is not enhanced by interactions.

We present GALEX FUV (1530 A) and NUV (2310 A) observations of the archetypal merging system NGC 4038/39, ``The Antennae". Both tails are relatively bright in the UV, especially in the vicinity of the Tidal Dwarf Galaxy candidates at the end of the southern tail. The UV light generally falls within the optically delineated tails, although the UV light is considerably more structured, with a remarkably similar morphology to the tidal HI. The UV colors suggest that there has been continuing star formation within the tidal tails, even outside the previously studied Tidal Dwarf regions. Within the inner disk regions, there are interesting UV features which appear to be related to the extended soft X-ray loops and halo recently discovered by CHANDRA.

We present Galaxy Evolution Explorer (GALEX) far-UV and near-UV mosaic observations covering the entirety of M31 and M33. For both targets, we measure the decline of surface brightness (in FUV and NUV) and changes in FUV--NUV color as a function of galactocentric radius. These UV radial profiles are compared to the distribution of ionized gas traced by H-alpha emission. We find that the extent of the UV emission, in both targets, is greater than the extent of the observed HII regions and diffuse ionized gas. We determine the ultraviolet diffuse fraction in M33 using our FUV observations and compare it to the H-alpha diffuse fraction obtained from wide-field narrow-band imaging. The FUV diffuse fraction appears to be remarkably constant near 0.65 over a large range in galactocentric radius, with departures to higher values in circumnuclear regions and, most notably, at the limit of the H-alpha disk. We suggest that the increase in FUV diffuse fraction at large galactocentric radii could indicate that a substantial portion of the diffuse emission beyond this point is not generated in situ but rather scattered from dust, after originating in the vicinity of the disk's outermost HII regions. Radial variation of the H-alpha diffuse fraction was also measured. We found the H-alpha diffuse fraction generally near 0.4 but rising toward the galaxy center, up to 0.6. We made no attempt to correct our diffuse fraction measurements for position-dependent extinction, so the quoted values are best interpreted as upper limits given the plausibly higher extinction for stellar clusters relative to their surroundings.

We present the results of a determination of the galaxy luminosity function at ultraviolet wavelengths at redshifts of $z=0.0-0.1$ from GALEX data. We determined the luminosity function in the GALEX FUV and NUV bands from a sample of galaxies with UV magnitudes between 17 and 20 that are drawn from a total of 56.73 deg^2 of GALEX fields overlapping the b_j-selected 2dF Galaxy Redshift Survey. The resulting luminosity functions are fainter than previous UV estimates and result in total UV luminosity densities of 10^(25.55+/-0.12) ergs s^-1 Hz^-1 Mpc^-3 and 10^(25.72+/-0.12) ergs s^-1 Hz^-1 Mpc^-3 at 1530 Ang. and 2310 Ang., respectively. This corresponds to a local star formation rate density in agreement with previous estimates made with H-alpha-selected data for reasonable assumptions about the UV extinction.

We present measurements of the UV galaxy luminosity function and the evolution of luminosity density from GALEX observations matched to the Sloan Digital Sky Survey (SDSS). We analyze galaxies in the Medium Imaging Survey overlapping the SDSS DR1 with a total coverage of 44 deg^2. Using the combined GALEX+SDSS photometry, we compute photometric redshifts and study the LF in three redshift shells between z=0.07 and 0.25. The Schechter function fits indicate that the faint-end slope alpha is consistent with -1.1 at all redshifts but the characteristic UV luminosity M* brightens by 0.2 mag from z=0.07 to 0.25. In the lowest redshift bin, early and late type galaxies are studied separately and we confirm that red galaxies tend to be brighter and have a shallower slope alpha than blue ones. The derived luminosity densities are consistent with other GALEX results based on a local spectroscopic sample from 2dF and the evolution follows the trend reported by deeper studies., This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We have used the GALEX UV photometric data to construct a first near-ultraviolet (NUV) color-magnitude relation (CMR) for the galaxies pre-classified as early-type by SDSS studies. The NUV CMR is a powerful tool for tracking the recent star formation history in early-type galaxies, owing to its high sensitivity to the presence of young stellar populations. Our NUV CMR for UV-weak galaxies shows a well-defined slope and thus will be useful for interpreting the restframe NUV data of distant galaxies and studying their star formation history. Compared to optical CMRs, the NUV CMR shows a substantially larger scatter, which we interpret as evidence of recent star formation activities. Roughly 15% of the recent epoch (z < 0.13) bright (M[r] < -22) early-type galaxies show a sign of recent (< 1Gyr) star formation at the 1-2% level (lower limit) in mass compared to the total stellar mass. This implies that low level residual star formation was common during the last few billion years even in bright early-type galaxies.

The Galaxy Evolution Explorer (GALEX) Nearby Galaxies Survey is providing deep far-UV and near-UV imaging for a representative sample of galaxies in the local universe. We present early results for M51 and M101, from GALEX UV imaging and Sloan Digital Sky Survey optical data in five bands. The multiband photometry of compact stellar complexes in M101 is compared to population synthesis models, to derive ages, reddening, reddening-corrected luminosities, and current/initial masses. The GALEX UV photometry provides a complete census of young compact complexes on a ≈160 pc scale. A galactocentric gradient of the far-UV/near-UV color indicates younger stellar populations toward the outer parts of the galaxy disks, the effect being more pronounced in M101 than in M51.

We present ultraviolet photometry for globular clusters (GCs) in M31 from 15 square deg of imaging using the Galaxy Evolution Explorer (GALEX). We detect 200 and 94 GCs with certainty in the near-ultraviolet (NUV; 1750 - 2750 Angstroms) and far-ultraviolet (FUV; 1350 - 1750 Angstroms) bandpasses, respectively. Our rate of detection is about 50% in the NUV and 23% in the FUV, to an approximate limiting V magnitude of 19. Out of six clusters with [Fe/H]>-1 seen in the NUV, none is detected in the FUV bandpass. Furthermore, we find no candidate metal-rich clusters with significant FUV flux, because of the contribution of blue horizontal-branch (HB) stars, such as NGC 6388 and NGC 6441, which are metal-rich Galactic GCs with hot HB stars. We show that our GALEX photometry follows the general color trends established in previous UV studies of GCs in M31 and the Galaxy. Comparing our data with Galactic GCs in the UV and with population synthesis models, we suggest that the age range of M31 and Galactic halo GCs are similar.

Number Counts of galaxies in two GALEX bands (FUV: 1530A and NUV: 2310A, both in AB magnitudes) are reported. They provide for the first time in the literature homogeneously calibrated number counts of UV galaxies covering continuously a very wide range of UV magnitude (14 -- 23.8). Both the FUV and NUV counts are inconsistent with a non-evolution model, while they are in good agreement with evolution models (essentially luminosity evolution) derived from the high-z UV luminosity functions of Arnouts et al. (2004). It is found that the contribution from galaxies detected by GALEX to the UV background is 0.68+-0.10 nW m-2 sr-1 at 1530A and 0.99+-0.15 nW m-2 sr-1 at 2310A. These are 66+-9% and 44+-6% of the total contributions of galaxies to the the UV background at 1530A, respectively, as estimated using the evolution models. ...

We have matched 358,046 objects in 143 deg2 of overlap between the Galaxy Evolution Explorer (GALEX) and the Sloan Digital Sky Survey (SDSS). This Letter provides matching statistics at Medium Imaging Survey and All-sky Imaging Survey depths for SDSS-classified stars and galaxies as well as spectroscopic star, galaxy, and QSO subsamples. Distributions of magnitudes, redshifts, and colors are provided. Near-ultraviolet (NUV)-based color-color diagrams reveal (1) the segregation of main-sequence, horizontal-branch, subdwarf, white dwarf, M dwarf, and M dwarf-white dwarf binary stellar populations, (2) a bimodal distribution of galaxies, and (3) the higher signal quality of the GALEX NUV compared to the SDSS u band.

We present an absorption study of the interstellar gas at high positive galactic latitudes in the direction close to the axis of the Local Chimney (LC), which is an extension of the rarefied local cavity that reaches out from the galactic disk to a z-distance of at least 250 pc into the lower halo region. Our study includes high-resolution (R ∼ 1. 7k m s −1 ) spectral observations of the interstellar NaI and CaII absorption lines seen towards 6 early-type stars with distances ranging from 225 to 500 pc contained within a radius of ∼6 ◦ along the sight-line (l = 160 ◦ , b =+ 55 ◦ ). These visible data are supplemented with far-ultraviolet absorption measurements of the interstellar sight-lines towards two hot white dwarf stars, RE J1043+490 (d = 230 pc) and RE J1059+512 (d = 315 pc), taken with the NASA Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Our observations reveal interstellar gas clouds with velocities in the −20 to −60 km s −1 range that appear to be falling towards the galactic disk. In particular, we have detected absorption with a velocity of Vhelio ∼− 55 km s −1 towards two sight-lines (HD 89501 and HD 88545) that can be associated with an intermediate velocity (IV) cloud called the IV Arch. Our observations place a probable z-distance to this IVC of 275-320 pc, this being much nearer than previously thought. The far UV spectra of the two hot white dwarfs show only a few (∼10) interstellar absorption lines, which is indicative of the very low density phase of the interstellar gas contained within the LC region. We have derived relative elemental abundance ratios for C, N, O, Si, Ar and Fe for these two sight-lines and find that the abundance patterns are very similar to those found for other sight-lines in the local cavity. The high ionization line of OVIλ1032 A has been detected towards RE J1043+490 with a column density of 7 × 10 12 cm −2 , which is consistent with the average space density of this ion recently found in the Local Bubble region. Finally, we (tentatively) propose a possible connection between the formation of the Gould Belt, the Local Bubble cavity, the Local Chimney and the overlying IV Arch clouds.

We present intermediate results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, motivated by the availability of accurate and consistent parallaxes from the Hipparcos satellite. Equivalent widths of the interstellar NaI D-line doublet at 5890 A are presented for the lines-of-sight towards some 311 new target stars lying within ∼350 pc of the Sun. Using these data, together with NaI absorption measurements towards a fur- ther ∼240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ∼450 lines- of-sight already presented by (Sfeir et al. 1999), we show 3D absorption maps of the local distribution of neutral gas towards 1005 sight-lines with Hipparcos distances as viewed from a variety of different galactic projections. The data are synthesized by means of two complementary methods, (i) by mapping of iso-equivalent width contours, and (ii) by density distribution calculation from the inversion of column-densities, a method devised by Vergely et al. (2001). Our present data confirms the view that the local cavity is deficient in cold and neutral interstellar gas. The closest dense and cold gas "wall", in the first quadrant, is at ∼55-60 pc. There are a few isolated clouds at closer distance, if the detected absorption is not produced by circumstellar material. The maps reveal narrow or wide "interstellar tunnels" which connect the Local Bubble to surrounding cavities, as predicted by the model of Cox & Smith (1974). In particular, one of these tunnels, defined by stars at 300 to 600 pc from the Sun showing negligible sodium absorption, connects the well known CMa void (Gry et al. 1985), which is part of the Local Bubble, with the supershell GSH 238+00+09 (Heiles 1998). High latitude lines-of-sight with the smallest absorption are found in two "chimneys", whose directions are perpendicular to the Gould belt plane. The maps show that the Local Bubble is "squeezed" by surrounding shells in a complicated pattern and suggest that its pressure is smaller than in those expanding regions. We discuss the locations of several HI and molecular clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints on their distances. According to the velocity criteria, MBM 33−37, MBM 16−18, UT 3−7, and MBM 54−55 are closer than ∼100 pc, and MBM 40 is closer than 80 pc. Dense HI clouds are seen at less than 90 pc and 85 pc in the directions of the MBM 12 and MBM 41−43 clouds respectively, but the molecular clouds themselves may be far beyond. The above closest molecular clouds are located at the neutral boundary of the Bubble. Only one translucent cloud, G192−67, is clearly embedded within the LB and well isolated. These maps of the distribution of local neutral interstellar NaI gas are also briefly compared with the distribution of both interstellar dust and neutral HI gas within 300 pc.

We present high-resolution spectra (R 1: 8k m s 1 ) of the interstellar NaI and CaII interstellar absorption lines observed towards 4 early-type stars with distances of 900-1500 pc in the line-of-sight towards the IC 443 Supernova Remant (SNR). The spectra of two of these stars (HD 43582 and HD 254577) exhibit a very complex pattern of absorption with cloud components covering a total velocity range of 100 km s 1 to+50 km s 1 . The relative absorption strength of many of the higher velocity components is highly variable between these two stars, suggesting that the disturbed interstellar gas in this region possesses significant density gradients and/or large dierences in ionization and element depletion. In addition, we have detected three additional high-velocity components at Vhelio = 97:5, 84.0 and 67.6 km s 1 solely in their CaII lines, suggesting that the very highest velocity gas is more ionized and/or warmer than the lower velocity components or it has a highly variable level of gas phase element abundances. The column density ratios of NaI/CaII for the higher velocity cloud components are all

An externally dispersed interferometer (EDI) is a series combination of a fixed delay interferometer and an external grating spectrograph. We describe how the EDI can boost the effective resolving power of an echelle or linear grating spectrograph by a factor of 2-3 or more over the spectrograph's full bandwidth. The interferometer produces spectral fringes over the entire spectrograph's bandwidth. The fringes heterodyne with spectral features to provide a low spatial frequency moire pattern. The heterodyning is numerically reversed to recover highly detailed spectral information unattainable by the spectrograph alone. We demonstrate resolution boosting for stellar and solar measurements of two-dimensional echelle and linear grating spectra. An effective spectral resolution of ~100,000 has been obtained from the ~50,000 resolution Lick Observatory two-dimensional echelle spectrograph, and that of ~50,000 from an ~20,000 resolution linear grating spectrograph.

We present medium resolution spectra ($R\sim 7$ km s -1 ) of the interstellar NaI D1 & D2 absorption lines observed towards 7 early-type stars with distances ranging from 221 to ~1.5 kpc in the line-of-sight to the RCW 114 nebula. Our observed pattern of absorption is in conflict with the findings of Bedford et al. (1984) who placed an upper limit to the distance to this nebula of 1 kpc. A similar pattern of absorption behavior is seen for the SiII λ 1304 A interstellar line observed in the ultraviolet towards four of the aforementioned stars. We propose a scenario in which the absorption components with velocities -1 seen towards RCW 114 are caused by an expanding stellar wind-blown bubble associated with the Wolf-Rayet (WR) star, HD 156385 ($d \sim 1.5$ kpc), and that the H α and [SII] nebular emission probably arises in shocked filamentary gas associated with a pre-existing evolved supernova remnant cavity produced by the high-mass progenitor of the present WR star.

We present Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) satellite measurements of the absorption and emission characteristics of interstellar gas associated with the Local Interstellar Chimney, which is an extension of the rarefied Local Bubble cavity that extends outward from the galactic disk towards the lower galactic halo. Far ultraviolet (FUV) diffuse background emission has been detected in the high ionization line of O VI ( λ 1032 A) for two lines-of-sight ($l = 162.7^{\circ}$, $b = +57.0^{\circ}$) and ($l = 156.3^{\circ}$, $b = +57.8^{\circ}$) at emission levels of $2500\pm700$ photons cm -2 s -1 sr -1 (LU) and $3300\pm1100$ LU respectively. These levels of O VI emission are very similar to those found for four other lines-of-sight sampled thus far by the $\it FUSE$ satellite, implying a fairly constant level of average O VI surface brightness emission at high galactic latitudes of about 2700 LU with a standard deviation of 450 LU. These emission-line data are supplemented by FUV interstellar absorption line measurements taken towards the hot DA white dwarf star, REJ 1032+532 ($l = 157.5^{\circ}$, $ b = +53.2^{\circ}$), whose distance of 116 pc places it within the Local Bubble region. No high ionization interstellar O VI λ 1032 A absorption has been detected $(N({\rm O~VI}) -2 ), which is consistent with the non-detections of interstellar C IV and Si IV absorption reported towards this star by Holberg et al. ([CITE]). Taken together, our FUV absorption and emission data may be explained by a scenario in which the O VI emission and absorption lines are $\it both$ formed at the conductive interface of the neutral boundary to the Local Bubble. For the presently sampled sight-lines we have found no correlation between the OVI emission line intensity and the associated 0.25 keV soft X-ray background flux as measured in the R1 and R2 bands by the $\it ROSAT$ satellite. The OVI line intensities also show no correlation with the soft X-ray background flux attributable to emission from the million degree K gas of the Local Hot Bubble as modeled by Kuntz & Snowden ([CITE]). Any (new) model of the Local Bubble must now be able to explain (i) the low levels of variability in both the O VI emission-line intensity and the associated soft X-ray background flux for galactic sight-lines > $|40|$°, (ii) the observed pressure of $P/k\sim 10\,000$ cm -3 K for the local hot interstellar gas, and (iii) the paucity of high ionization absorption lines observed within the local ISM and the sudden increase in their measured column density for distances beyond the Local Bubble neutral boundary.