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.
This catalogue is an updated version of the one published in 1990 (Hauck and Mermilliod, 1990) and contains data for more than 63,300 stars in the Galaxy and Magellanic Clouds. In a first table, we present the catalogue itself, giving for each star identifications, coordinates (B1950), visual magnitude, and the mean value of the photoelectric data concerning the star and the data sources. In the second table, we give for each star, the individual measurements. These measurements from which these values were computed were collected from observations published until the middle of 1996. The catalogue includes 533 references.
A uvbyH{beta} Stromgren photometric survey covering 16sq.deg in the anticenter direction was carried out using the Wide Field Camera (WFC) at the Isaac Newton Telescope (INT), with a typical seeing of 1-1.5". Data from three different observing runs (2009A, 2010B, 2011A) were used for the catalog. The calibration to the standard system was undertaken using open clusters. A main catalog of 35974 stars with all Stromgren indexes, and a more extended one with 96980 stars with partial data. The central 8sq.deg have a limiting magnitude of V=17mag while the outer region reaches V=15.5mag. Two catalogs are available, the first one with the final mean values and a second one with all the individual measurements for each star.
In recent years a significant development has become evident in the study of the stellar structure of the Galactic disk. This is especially true for the 3rd Galactic quadrant, where the stellar population was extensively investigated beyond 10kpc, revealing details about the warped geometry of the thin and thick disks and outer arm. The 4th Galactic quadrant offers even better opportunity to follow the distribution of the young stellar populace to a large distance, since the line of sight is parallel to the largest single segment of a spiral arm seen from our position in the Galaxy: the Carina spiral feature. This paper further contributes to the study of the structure of the Galactic disk in the direction of Carina field utilizing homogeneous photometric distances of a sample of about 600 bright early-type stars seen in this direction up to 6kpc. The derived stellar distances are based on uvby{beta} photometry. All O and B type stars with uvby{beta} data presently available are included in the study.
Stroemgren uvby{beta} photometry has been collected for a total of 1017 stars earlier than G0 lying in an area of the sky containing the Southern Coalsack, the Musca, and the Chamaeleon dark clouds. The targets were selected from the SAO star catalog, and the results give V, b-y, m_1_, c_1_, and {beta} on the standard systems, with overall rms errors for one observation of one star of 0.008mag , 0.004mag , 0.006mag , 0.009mag , and 0.011mag , respectively.
We present the uvby{beta} data used to locate the dust and derive distances for nearby diffuse interstellar clouds in the EUV shadows lb27-31, lb165-32 and lb329+46 discovered by the Extreme Ultraviolet Explorer. The photometrically derived parallaxes of our program stars are compared to the parallaxes listed in the Hipparcos Catalog. Within the photometric distance limit of 150pc, the photometric parallaxes of 21 ``normal" stars are consistent with the Hipparcos measurements within an uncertainty of 15%. Much as expected for the Stroemgren system. Since all program stars are brighter than V=~11.5 most of them are included in the Tycho photometry. For our sample of ~200 stars we find V_by_ and V_T_ to be consistent. Few stars are common to published uvby{beta} catalogs, ~10, V and the indices compare well apart from {beta} where a zero point difference of 11mmag is noticed.
This investigation presents a study of the Galactic structure toward the Norma section of the Milky Way. The field studied is located between 325{deg} and 335{deg} Galactic longitude and -8{deg} to 8{deg} Galactic latitude. New observations in the uvby{beta} system are combined with all uvby{beta} data currently available to collate a sample of 130 O and B stars. A uniform procedure is applied to obtain the color excesses and stellar distances for all of the stars in the sample. The sample is magnitude limited to about V=9.5mag and contains the brightest stars of the open clusters NGC 6087 and Ly 6, the field 2158 of Loden, the OB association Nor OB1, and stars located in the directions of R 103 and R 105.
Results are presented of Stromgren uvby(beta) photometry for 213 stars earlier than G0 and brigher than mpg of about 10.7mag in Selected Area 203. The observed area lies close to the geometric center of the Chamaeleon-Musca dark clouds complex. The results yield V, (b-y), m1, c1, and beta on the standard systems, with overall rms errors for one observation of one star of 0.010, 0.004, 0.007, 0.009, and 0.011, respectively.
Photometric color excesses and distances plus heliocentric coordinates are calculated for 3762 southern A and early-F stars. The present results, combined with those previously published for the Northern Hemisphere, complete the coverage of the spatial distribution of interstellar reddening in the entire solar neighborhood. The new reddening maps show that the interstellar matter within 300pc of the Sun forms a single very large cloud complex that is somewhat asymmetrical with respect to both the galactic center and the galactic plane. This complex is characterized by pronounced local irregularities in both density and spatial extent. The observations further indicate that (1) the cloud complex is not associated with Gould's belt; (2) there exist large regions of the sky devoid of dust; (3) interstellar reddening is negligible at the galactic poles; (4) the role of intercloud dust in the Southern Hemisphere is minor although more important than in the Northern Hemisphere; (5) the Sun is not located in a dust-free, spherically symmetric bubble as previously thought; and (6) the Sun is, however, located in an elongated dust-free region known as the "local trough."
