J/AJ/111/1128 UV-UBV photometry in NGC 595 (Malumuth+ 1996)
The stellar initial mass function in the giant H II region NGC 595
Malumuth E.M., Waller W.H., Parker J.Wn.
<Astron. J. 111, 1128 (1996)>
=1996AJ....111.1128M 1996AJ....111.1128M
ADC_Keywords: H II regions ; Photometry, UBV ; Photometry, ultraviolet
Abstract:
As part of a larger effort to study the resolved and composite
properties of the giant H II regions in Messier 33, we have analyzed
multiband HST/WFPC-2 images of NGC 595 in terms of the ionizing
cluster's resolved stellar population. Photometric reductions of the
PC images yield 100 stars in the UV image, 272 stars on the U image,
345 stars on the B image, and 561 stars on the V image. A total of 267
stars are common to the U, B, and V images while 86 stars are detected
on all 4 images. Although some clustering is evident, the degree of
central concentration is less than that seen in 30 Doradus. The
resulting U-B vs B-V diagram of the resolved stars is used to
determine the reddening of each star. The average reddening derived
from this diagram is E(B-V)=0.36±0.28mag. The dereddened color-M_V
diagram is best fit by a model cluster having an age of 4.5±1.0Myr,
and hence initial masses no greater than 51M☉. A total of 13
supergiant stars and 10 candidate WR stars
[Drissen et al. (1993AJ....105.1400D 1993AJ....105.1400D), and references therein] are
identified with M_V=-5 to -8mag. The remainder are main-sequence
O-type (98) and early B-type (>145) stars with M_V=-1 to -6mag. The
ratio of WR to O stars is WR/O=0.11±0.01, roughly the same as found
in the core of 30 Doradus. The resulting luminosity function has a
slope of alpha=-0.71. The derived IMF has a slope of
Gamma=-1.32±0.02 before subtracting a background component, and
Gamma=-1.00±0.05 after subtracting a background based on photometry
of the surrounding WF images. Integration of the derived IMF down to a
lower mass limit of 4M☉ yields a total mass of 7350M☉,
while integration down to 0.1{Msun} yields a total mass of
18000M☉. The total estimated ionizing luminosity is
5.0x10^50photon/s, roughly half that which is inferred from the Halpha
luminosity in this region. This shortfall of ionizing photons can be
reconciled by allowing for a spread in the stellar ages, and/or
increasing the modeled EUV luminosity of the stars at the inferred
cluster age.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 62 573 NGC 595 photometry
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID Identification number
5- 8 I4 --- DMS []? Star number from table 1 of Drissen et al.
(1993AJ....105.1400D 1993AJ....105.1400D)
11- 12 I2 h RAh Right ascension, J2000
14- 15 I2 min RAm Right ascension, J2000
17- 21 F5.2 s RAs Right ascension, J2000
24 A1 --- DE- Declination sign
25- 26 I2 deg DEd Declination, J2000
28- 29 I2 arcmin DEm Declination, J2000
31- 34 F4.1 arcsec DEs Declination, J2000
36- 41 F6.2 mag UVmag []? Ultraviolet magnitude (F170W HST filter)
43- 48 F6.2 mag Umag []? U magnitude
50- 55 F6.2 mag Bmag []? B magnitude
57- 62 F6.2 mag Vmag []? V magnitude
--------------------------------------------------------------------------------
Origin: AAS CD-ROM series, Volume 6, 1996 Lee Brotzman [ADS] 02-May-1996
(End) [CDS] 05-Sep-1996