Ultraviolet photometry is presented for the globular cluster M79 (NGC 1904) according to the final calibration of the images obtained on the Astro-1 Spacelab mission by the Ultraviolet Imaging Telescope. These results include both point-source and surface photometry at 152nm and 249nm. An ultraviolet color-magnitude (C-M) diagram in these bandpasses is presented. The detected stars are also cross-matched with the ground-based photometry of Ferraro et al. (1992MNRAS.256..391F) to produce C-M and two-color diagrams covering a 4000A span in wavelength. The observed horizontal branch (HB) is compared with stellar interior models of the zero-age HB (ZAHB). Many stars are found in post-HB evolutionary stages more luminous than the ZAHB. The distribution of stars along the ZAHB in m152-m249 color is investigated, and an indication of possible bimodality is found. The relative population of the blue HB tail may vary with radius for radii greater than 1'. Ultraviolet surface brightness and color-index profiles are presented. The previously reported central gradient in the m152-V color index is confirmed, and a faint diffuse component is detected outside a radius of 40" in the 152nm band. Two possible causes of the central color gradient are discussed: mass segregation, and the destruction of red giant envelopes by enhanced mass loss in the cluster core.
We present U, V photometry of the globular cluster M2. Stars within 1' and outside of 4' from the cluster center are excluded from the CMD to reduce blending effects and the field star contamination, respectively. We imposed on all stars the selection limits of CHI<2.0 and -1<SHARP<1 on DAOPHOT II photometric parameters. To select a sample of well-measured stars we have followed the procedure given in Lardo et al. (2012A&A...541A.141L), Sect. 5.1. M2 photometry displays an anomalous branch beyond the red edge of the main body of the RGB. The difference in color between stars belonging to this structure and normal RGB stars is quite large (of the order of 0.2-0.3mag, well above the typical measurement errors) and extends down to the SGB region. There may be a second group of stars that are 0.3mag redder with respect to this sequence and can possibly be more, anomalous RGB stars. The observations were carried out during the nights of 2010 July 15 at the Telescopio Nazionale Galileo (TNG) located in La Palma, Canary Islands (Spain), with he DOLORES camera. The DOLORES camera offers a field of view of 8.6'x8.6' with a 0.252"/pix scale. We obtained images of the cluster in the standard Johnson U and V filters for a total of 540s shifted in 3 single exposures in each filter. The seeing condition were average during (~1.2-1.3") during the observing night.
We examine new observations of NGC 2808, taken with the far-UV and near-UV cameras on the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). Images were obtained in the far-UV crystal quartz (FUV/F25QTZ; pivot wavelength 1600{AA}), near-UV 2700{AA} continuum (NUV/F25CN270), and clear CCD (CCD/50CCD; pivot wavelength 5850{AA}) modes, employing a cross-shaped dither pattern.
We present a catalog of 36120 QSO candidates from the Galaxy Evolution Explorer (GALEX) Release Two (GR2) UV catalog and the USNO-A2.0 optical catalog. The selection criteria are established using known quasars from the Sloan Digital Sky Survey (SDSS). The SDSS sample is then used to assign individual probabilities to our GALEX USNO candidates. The mean probability is ~50% and would rise to ~65% if better morphological information than that from USNO were available to eliminate galaxies. The sample is ~40% complete for i<=19.1. Candidates are cross identified in 2MASS, FIRST, SDSS, and the XMM-Newton Slewing Survey (XMMSL1), whenever such counterparts exist. The present catalog covers the 8000deg^2^ of GR2 lying above |b|=25{deg}, but can be extended to all 24000deg^2^ that satisfy this criterion as new GALEX data become available.
We have obtained deep FUV and NUV images of the inner region of the dense globular cluster M15 with the HST ACS. The FUV-NUV color-magnitude diagram shows a well-defined track of horizontal branch stars, as well as a trail of blue stragglers and white dwarfs. The main-sequence turnoff is clearly visible at FUV~22.5mag and FUV-NUV~3mag, and the main-sequence stars form a prominent track that extends at least 2mag below the main-sequence turnoff. As such, this is the deepest FUV-NUV color-magnitude diagram of a globular cluster presented so far. Cataclysmic variable and blue straggler candidates are the most centrally concentrated stellar populations, which might either be an effect of mass segregation or reflect the preferred birthplace in the dense cluster core of such dynamically formed objects. We find 41 FUV sources that exhibit significant variability. We classify the variables based on an analysis of their UV colors and variability properties. We find four previously known RR Lyrae and 13 further RR Lyrae candidates, one known Cepheid and six further candidates, six cataclysmic variable candidates, one known and one probable SX Phoenicis star, and the well-known low-mass X-ray binary AC 211. Our analysis represents the first detection of SX Phoenicis pulsations in the FUV. We find that Cepheids, RR Lyrae stars, and SX Phoenicis exhibit massive variability amplitudes in this wave band (several magnitudes).
The core of the nearby and very concentrated globular cluster NGC 6397 has been imaged through the f/96-F140W, f/48-F140W, f/96-F210M and f/48-F220W ultraviolet filters of the Faint Object Camera on board the Hubble Space Telescope down to an ultraviolet limiting magnitude of ~19. The most interesting objects in the field of view are six very bright centrally concentrated, blue stragglers observed for the first time in the UV. Using these and other data from ground-based observations, we have been able to deduce from a comparison with Kurucz's atmosphere models, temperatures of ~10000K and masses of ~1.6M_{sun}_ for the four brightest ones, which is remarkably close to twice the turn-off mass of NGC 6397. This finding supports the idea that two-star mechanisms (collisions, mergers) are at the origin of the blue stragglers in the core of NGC 6397. Since the central density is very high, collisions between main sequence stars are frequent, therefore providing the best formation mechanism. We have computed the number of such collisions in the core of NGC 6397 and found it to be of the same order as the number of bright blue stragglers observed there. Thanks to the HST resolution, we have also been able to resolve one object, previously classified as a yellow straggler, into a blend of a blue straggler and three redder stars.
A statistical study is presented of (1) the frequency of narrow C IV {lambda}1549 absorption lines in 1.5<=z<~3.6 radio-quiet and radio-loud quasars and (2) the UV and radio properties of the absorbed quasars. The quasar sample is unbiased with respect to absorption properties, and the radio-quiet and radio-loud subsamples are well matched in redshift and luminosity.
We present Galaxy Evolution Explorer (GALEX) data for 44 Galactic globular clusters (GCs) obtained during three GALEX observing cycles between 2004 and 2008. This is the largest homogeneous data set on the UV photometric properties of Galactic GCs ever collected. The sample selection and photometric analysis are discussed, and color-magnitude diagrams (CMDs) are presented. The blue and intermediate-blue horizontal branch is the dominant feature of the UV CMDs of old Galactic GCs. Our sample is large enough to display the remarkable variety of horizontal branch shapes found in old stellar populations. Other stellar types that are obviously detected are blue stragglers and post-core-He burning stars. The main features of UV CMDs of Galactic GCs are briefly discussed. We establish the locus of post-core-He burning stars in the UV CMD and present a catalog of candidate asymptotic giant branch (AGB), AGB-manque, post early-AGB, and post-AGB stars within our cluster sample.
In the last decade several satellite and balloon borne experiments have collected a large number of ultraviolet fluxes of normal galaxies measured through apertures of various sizes and shapes. We have homogenized this data set by deriving scale corrections with respect to IUE. In a forthcoming paper, these data will be used to derive standard luminosity profiles and total magnitudes.
In the previous papers of this series (Longo et al. =1991A&AS...90..375L; Rifatto et al. =1995A&AS..109..341R) we collected and reduced to the same system all the available photometric data obtained in the ultraviolet (UV) range for normal (i.e. non active) galaxies. Here we use these data to derive standard UV luminosity profiles for three morphological bins (E/S0; Sa/Sb; Sc/Sd) and extrapolated total magnitudes for almost 400 galaxies. We find that: 1) the UV growth curves are well matched by the B-band revised standard luminosity profiles, once a proper shift in the effective radius is applied, and 2) the UV light in early-type galaxies is more centrally concentrated than the visible light.
