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1. Magellanic clouds ultraviolet observations
ID:
ivo://CDS.VizieR/J/AJ/116/180
Title:
Magellanic clouds ultraviolet observations
Short Name:
J/AJ/116/180
Date:
21 Oct 2021
Publisher:
CDS
Description:
The catalog is derived from wide-field far-ultraviolet (FUV; 1300-1800{AA}) images of the Large and Small Magellanic Clouds (LMC, SMC) obtained by the Ultraviolet Imaging Telescope (UIT) during the Astro-1 (1990 December 1-10) and Astro-2 (1995 March 2-18) missions. The FUV magnitudes are derived from point-spread function photometry for 37,333 stars in the LMC (the UIT FUV magnitudes for 11,306 stars in the SMC were presented by Cornett et al. (1997AJ....113.1011C), with a completeness limit of m_UV_ ~ 15mag and a detection limit of m_UV_ ~ 17.5. The average uncertainty in the photometry is ~ 0.1mag.
2. Omega Cen FUV photometry
ID:
ivo://CDS.VizieR/J/AJ/108/1350
Title:
Omega Cen FUV photometry
Short Name:
J/AJ/108/1350
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present far-ultraviolet images of the globular cluster {omega} Centauri obtained with the Ultraviolet Imaging Telescope (UIT) during the 1990 December Astro-1 mission. A total of 1957 sources are detected at 1620{AA} to a limiting UV magnitude of 16.4 in the central 24' diameter region of the field and a limit of 15.6 over the remainder of the 40' diameter field. Over 1400 of these sources are matched with stars on a Stroemgren u band CCD frame obtained with the CTIO 0.9m telescope to produce a (far-UV, u) color-magnitude diagram. Completeness of the sample and error estimates are determined by photometry of artificial stars added to the images. The horizontal branch (HB) of the CMD is heavily populated hotter than 9000K. A large number of "extreme HB" stars are found hotter than a conspicuous break in the HB at Te~16000K. There is also a significant population of stars above the HB, the brightest of which is 4mag brighter than the HB. Most of the hotter of these appear to be "AGB-manque" or "Post-Early Asymptotic Giant Branch" stars. We compare the observations to recent theoretical evolutionary tracks for the zero-age HB and subsequent phases. The tracks match the data well, with the exception of the hotter HB stars, many of which fall below the zero-age horizontal branch. It is unclear as yet whether these are a special population or an artifact of errors in the models or photometry. We identify 33 stars with Te>~50000K, which are hotter than zero-age HB stars with envelope masses of 0.003M_{sun}_.
3. UIT near-UV bright objects catalog
ID:
ivo://CDS.VizieR/J/ApJS/104/287
Title:
UIT near-UV bright objects catalog
Short Name:
J/ApJS/104/287
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a photometric catalog of 2244 objects detected by the Ultraviolet Imaging Telescope in the near-ultraviolet (NUV; 1650A<lambda<2900A) during the Astro-1 Space Shuttle mission. Sources in the catalog are as faint as m_nuv~18.8, or f_nuv~1.1x10^-16ergs/s/cm^2/A, but the survey is not complete to this level. Optical catalogs were used to cross identify sources and derive NUV-V colors. A majority of the objects (88%) do indeed have proposed optical identifications from catalogs, and most are stars. Our purpose in creating the catalog is to form a database useful for identifying very blue objects and performing Galactic UV stellar population studies.
4. UV-brightest stars of M33 and its nucleus
ID:
ivo://CDS.VizieR/J/ApJ/469/629
Title:
UV-brightest stars of M33 and its nucleus
Short Name:
J/ApJ/469/629
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the UV-brightest sources in the nearby galaxy M33. Our catalog of 356 sources is constructed from far-ultraviolet (FUV; 1500A) and near-ultraviolet (NUV; 2400A) images obtained with the Ultraviolet Imaging Telescope (UIT) matched with ground-based UBV data. We find that our survey is limited by the FUV flux and is complete to F_1500=2.5x10^-15ergs/cm^2^/s/A, other than in the most crowded regions; this corresponds roughly to Mbol=-9.2 to -10.0 (or masses of 40-60M_{sun}_), for Teff=50,000{deg} to 10,000{deg}. We use Hubble Space Telescope (HST) WFPC2 images of several M33 fields to conclude that at least one-half of our sample is uncontaminated by unresolved neighbors, at least at the 0.1" (0.4pc) level, a resolution similar to that achieved in the LMC from the ground. Spectral types have been obtained for 131 of our objects. We discuss the spatial distribution of the UIT sources, finding that they provide an excellent tracer of the spiral arm pattern and confirm that star formation continues in the nuclear region to the present day. Our survey has found a large number of O and early B-type supergiants, including stars as early as O6, but the optical spectroscopic sample is dominated by later type B supergiants, as these are the visually brighter. Among the brightest stars (both at 1500A and at V) are the "superluminous" Wolf-Rayet stars first discovered by Conti & Massey in the largest H II regions of M33; these objects are now known to be small groups of stars in modest analog to R136 in 30 Dor. In general, our survey has failed to detect the known W-R stars, as they are too faint, but we did find several new late-type WN stars and composite systems, which are brighter. Two stars of high absolute visual magnitude (M_v~-9.0) are found to be B I + WN binaries, similar to HDE 269546 in the LMC; one of these is multiple at HST resolution. Most interesting, perhaps, is our finding six Ofpe/WN9 "slash" stars, five of them newly discovered. These stars show properties intermediate between those of Of and WN stars and are believed to be a quiescent form of luminous blue variables (LBVs). Our spectroscopy found five additional stars that are spectroscopically similar to the known LBVs of M33. One of these stars has recently been shown to be spectroscopically variable, and we suggest that all of these stars deserve continued scrutiny. The nucleus of M33 is the visually brightest object in our survey, and its UV colors are indicative of a hotter component than its optical photometry or spectral type would suggest. We discuss the possibility that the pointlike nucleus may contain a few interesting hot stars that dominate the light in the UV, and we make the comparison to the cluster of He I emission-line stars found near the center of the Milky Way. We comment on which color-magnitude and color-color plots make the best diagnostic tools for studying the hot, massive star population of a galaxy like M33.
5. UV Observations of the SMC
ID:
ivo://CDS.VizieR/J/AJ/113/1011
Title:
UV Observations of the SMC
Short Name:
J/AJ/113/1011
Date:
21 Oct 2021
Publisher:
CDS
Description:
A mosaic of four UIT (Ultraviolet Imaging Telescope) far-UV (FUV) ({lambda}_(eff)_=1620{AA}) images, with derived stellar and H II region photometry, is presented for most of the Bar of the SMC. The UV morphology of the SMC's Bar shows that recent star formation there has left striking features including: (a) four concentrations of UV-bright stars spread from northeast to southwest at nearly equal (~30arcmin=0.5kpc) spacings; (b) one of the concentrations, near DEM 55, comprises a well-defined 8-arcmin diameter ring surrounded by a larger H{alpha} ring, suggestive of sequential star formation. FUV PSF photometry is obtained for 11,306 stars in the FUV images, resulting in magnitudes m(162). We present a FUV luminosity function for the SMC Bar, complete to m(162)~14.5. Detected objects are well correlated with other SMC Population I material; of 711 H{alpha} emission-line stars and small nebulae within the UIT fields of view, 520 are identified with FUV sources. The FUV photometry is compared with available ground-based catalogs of supergiants, yielding 191 detections of 195 supergiants with spectral type earlier than F0 in the UIT fields. The (m(162)-V) color for supergiants is a sensitive measure of spectral type. The bluest observed colors for each type agree well with colors computed from unreddened Galactic spectral atlas stars for types earlier than about A0; for later spectral types the observed SMC stars range significantly bluer, as predicted by comparison of low-metallicity and Galactic-composition models. Redder colors for some stars of all spectral types are attributed to the strong FUV extinction arising from even small amounts of SMC dust. Internal SMC reddenings are determined for all catalog stars. All stars with E(B-V)>0.15 are within regions of visible H{alpha} emission. FUV photometry for 42 H{alpha} -selected H II regions in the SMC Bar is obtained for stars and for total emission (as measured in H II-region-sized apertures). The flux-weighted average ratio of total to stellar FUV flux is 2.15; consideration of the stellar FUV luminosity function indicates that most of the excess total flux is due to scattered FUV radiation, rather than stars fainter than m(162)=14.5. Both stellar and total emission are well correlated with H{alpha} fluxes measured by Kennicutt and Hodge (1986ApJ...306..130K), yielding FUV/H{alpha} flux ratios that are consistent with models of SMC metallicity, ages from 1-5Myr, and moderate (E(B-V)=0.0-0.1mag) internal SMC extinction. (Copyright) 1997 American Astronomical Society.
6. UV photometry in M79
ID:
ivo://CDS.VizieR/J/AJ/112/601
Title:
UV photometry in M79
Short Name:
J/AJ/112/601
Date:
21 Oct 2021
Publisher:
CDS
Description:
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.

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