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J/AJ/113/1011 UV Observations of the SMC (Cornett+ 1997)
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UIT: Ultraviolet Observations of the Small Magellanic Cloud
Cornett R.H., Greason M.R., Hill J.K., Parker J.W., Waller W.H.,
Bohlin R.C., Cheng K.-P., Neff S.G., O'Connell R.W., Roberts M.S.,
Smith A.M., Stecher T.P.
<Astron. J. 113, 1011 (1997)>
=1997AJ....113.1011C
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ADC_Keywords: Magellanic Clouds ; Photometry, ultraviolet
Mission_Name: UIT
Abstract:
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.
Description:
The table data were referred to, but did not appear in, the printed paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 58 11306 UIT FUV magnitudes of 11306 stars
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See also:
J/AJ/116/180 : Magellanic clouds ultraviolet observations (Parker+ 1998)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Star UIT star number
7 I1 --- Field *[1/4] UIT field number
9- 14 F6.1 pix Xpos *X pixel coordinate
16- 21 F6.1 pix Ypos *Y pixel coordinate
24- 25 I2 h RAh Right ascension (2000)
27- 28 I2 min RAm Right ascension (2000)
30- 33 F4.1 s RAs *Right ascension (2000)
36 A1 --- DE- Sign declination
37- 38 I2 deg DEd Declination (2000)
40- 41 I2 arcmin DEm Declination (2000)
43- 44 I2 arcsec DEs *Declination (2000)
46- 51 F6.2 mag m162 *m(162) derived from PSF photometry
53- 58 F6.2 mag e_m162 *Estimated error in m162
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Note on Field:
Fields are 40 arcmin in diameter; locations of Fields 1, 2, 3,
and 4 are shown in the printed paper.
Note on Xpos, Ypos:
1 pix = 1.12 arcsec; North is up, East left
Note on RAs, DEs:
Mean uncertainty in UIT positions is approximately 5 arcsec,
with smaller values near field centers (X=1023.5, Y=1023.5) and
larger values near the edges.
Note on m162:
UIT magnitudes are defined by
m({lambda})=-2.5 log(F({lambda})) - 21.1
where F({lambda}) is in units of ergs/cm^2^/Angstrom/s (mW/m^2^/Angstrom)
and is the mean flux per Angstrom over the UIT bandpass.
The magnitudes in this table are made with UIT's 'B5' bandpass,
which has an effective wavelength (for a flat input spectrum)
of 1620 Angstroms, and an effective width of 225 Angstroms.
These magnitudes are termed 'm(162)' (and occasionally 'm(B5)')
in the literature. More details on UIT hardware, observations,
and data reduction are in Stecher et al. (1992ApJ...395L...1S)
and in Stecher et al. (1997PASP..109..584S).
Note on e_m162:
This is the uncertainty returned by UITPHOT, an IDL/UIT
implementation of DAOPHOT which incorporates the noise
characteristics of UIT. It includes sky and other photometric
uncertainties, but no absolute calibration uncertainty. From
comparison with IUE spectra, the uncertainty in the absolute
calibration is about 0.15 for typical stars in this table.
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Origin: AAS CD-ROM series, Volume 8, 1997 Lee Brotzman [ADS] 09-Apr-1997
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(End) [CDS] 04-Jul-1997