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J/ApJ/469/629        UV-brightest stars of M33 and its nucleus (Massey+ 1996)

The UV-brightest stars of M33 and its nucleus: discovery, photometry, and optical spectroscopy Massey P., Bianchi L., Hutchings J.B., Stecher T.P. <Astrophys. J. 469, 629 (1996)> =1996ApJ...469..629M
ADC_Keywords: Photometry, UBV ; Photometry, ultraviolet Mission_Name: UIT Keywords: galaxies: individual (M33) - galaxies: stellar content - stars: early-type - stars: Wolf-Rayet - ultraviolet: stars Abstract: 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/cm2^/s/A, other than in the most crowded regions; this corresponds roughly to Mbol=-9.2 to -10.0 (or masses of 40-60M), for Teff=50,000° to 10,000°. 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. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 120 356 UIT sources in M33
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 6 A6 --- Star Source name 8- 9 I2 h RAh Right ascension, J2000 11- 12 I2 min RAm Right ascension, J2000 14- 18 F5.2 s RAs Right ascension, J2000 19 A1 --- DE- Declination sign, always blank 20- 21 I2 deg DEd Declination, J2000 23- 24 I2 arcmin DEm Declination, J2000 26- 29 F4.1 arcsec DEs Declination, J2000 31- 32 I2 --- N3 *Number of stars within 3" of V counterpart 34- 35 I2 --- N5 *Number of stars within 5" of V counterpart 37- 41 F5.2 mag FUV FUV magnitude 43- 47 F5.2 mag FUV-NUV FUV-NUV color 49- 53 F5.2 mag Vmag V magnitude 55- 59 F5.2 mag U-B U-B color index 61- 65 F5.2 mag B-V B-V color index 67- 71 F5.2 mag FUV-V FUV-V color index 73- 87 A15 --- Sp Spectral type 89-120 A32 --- Comment *Comments, cross IDs, indication of crowding
Note on N3: Total number of stars found on V image within 3" of the UIT V counterpart position. Note on N5: Total number of stars found on V image within 5" of the UIT V counterpart position. Note on Comment: Cross-identifications given in the Comments are: Halpha designation is from the unpublished Halpha survey described by Neese et al. (1991, IAU Symp. 143), the full text of which is in preparation B: stars from the list of blue stars in M33 by Humphreys & Sandage, 1980ApJS...44..319H. HSanon: unlisted blue stars on their finding charts, which also form the basis of describing a star as being inside a given OB association. obnn-xxx: stars from Massey et al., 1995AJ....110.2715M (Cat. J/AJ/110/2715) MC: refers to Massey & Conti, 1983ApJ...273..576M, W-R stars CM: refers to Conti & Massey, 1981ApJ...249..471C, stars in H II regions W91: refers to stars listed by Wilson, 1991AJ....101.1663W AM: stars are W-R stars found by Armandroff & Massey, 1985ApJ...291..685A MJ: refers to a recent deep survey for W-R stars by Massey & Johnson, 1996, in preparation N: refers to H II regions with NGC designations.
Origin: AAS CD-ROM series, Volume 7, 1996 Lee Brotzman [ADS] 22-Oct-96
(End) [CDS] 03-Feb-1997
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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