142 research outputs found
Resolving SNR 0540-6944 from LMC X-1 with Chandra
We examine the supernova remnant (SNR) 0540-697 in the Large Magellanic Cloud
(LMC) using data from the Chandra ACIS. The X-ray emission from this SNR had
previously been hidden in the bright emission of nearby X-ray binary LMC X-1;
however, new observations with Chandra can finally reveal the SNR's structure
and spectrum. We find the SNR to be a thick-shelled structure about 19 pc in
diameter, with a brightened northeast region. Spectral results suggest a
temperature of 0.31 keV and an X-ray luminosity (0.3-3.0 keV) of 8.4 x 10^33
erg/s. We estimate an age of 12,000-20,000 yr for this SNR, but note that this
estimate does not take into account the possibility of cavity expansion or
other environmental effects.Comment: 8 pages, 2 GIF figures. Submitted to ApJL. Replaced with minor
revisions from referee comment
Detections of massive stars in the cluster MCM2005b77, in the star-forming regions GRS G331.3400.36 (S62) and GRS G337.9200.48 (S36)
Large infrared and millimeter wavelength surveys of the Galactic plane have
unveiled more than 600 new bubble HII regions and more than 3000 candidate star
clusters. We present a study of the candidate clusters MCM2005b72, DBS2003-157,
DBS2003-172, and MCM2005b77, based on near-infrared spectroscopy taken with
SofI on the NTT and infrared photometry from the 2MASS, VVV, and GLIMPSE
surveys. We find that (1) MCM2005b72 and DBS2003-157 are subregions of the same
star-forming region, HII GRS G331.34-00.36 (bubble S62). MCM2005b72 coincides
with the central part of this HII region, while DBS2003-157 is a bright
mid-infrared knot of the S62 shell. We detected two O-type stars at extinction
\Aks=1.0-1.3 mag. Their spectrophotometric properties are consistent with the
near-kinematic distance to GRS G331.34-00.36 of 3.9pm0.3 kpc. (2) DBS2003-172
coincides with a bright mid-infrared knot in the S36 shell (GRS G337.92-00.48),
where we detected a pair of candidate He I stars embedded in a small cometary
nebula. (3) The stellar cluster MCM2005b77 is rich in B-type stars, has an
average Aks of 0.91 mag, and is adjacent to the HII region IRAS 16137-5025. The
average spectrophotometric distance of kpc matches the
near-kinematic distance to IRAS 16137-5025 of 5.2pm0.1 kpc.Comment: 22 pages, 11 Figures, ApJ accepte
A Critical Examination of Hypernova Remnant Candidates in M101. II. NGC 5471B
NGC 5471B has been suggested to contain a hypernova remnant because of its
extraordinarily bright X-ray emission. To assess its true nature, we have
obtained high-resolution images in continuum bands and nebular lines with the
Hubble Space Telescope, and high-dispersion long-slit spectra with the Kitt
Peak National Observatory 4-m echelle spectrograph. The images reveal three
supernova remnant (SNR) candidates in the giant HII region NGC 5471, with the
brightest one being the 77x60 pc shell in NGC 5471B. The Ha velocity profile of
NGC 5471B can be decomposed into a narrow component (FWHM = 41 km/s) from the
background HII region and a broad component (FWHM = 148 km/s) from the SNR
shell. Using the brightness ratio of the broad to narrow components and the Ha
flux measured from the WFPC2 Ha image, we derive an Ha luminosity of
(1.4+-0.1)x10^39 ergs/s for the SNR shell. The [SII]6716,6731 doublet ratio of
the broad velocity component is used to derive an electron density of ~700
cm^-3 in the SNR shell. The mass of the SNR shell is thus 4600+-500 Mo. With a
\~330 km/s expansion velocity implied by the extreme velocity extent of the
broad component, the kinetic energy of the SNR shell is determined to be
5x10^51 ergs. This requires an explosion energy greater than 10^52 ergs, which
can be provided by one hypernova or multiple supernovae. Comparing to SNRs in
nearby active star formation regions, the SNR shell in NGC 5471B appears truly
unique and energetic. We conclude that the optical observations support the
existence of a hypernova remnant in NGC 5471B.Comment: 27 pages, 9 figures, to appear in May 2002 issue of The Astronomical
Journa
Near-infrared spectroscopy of candidate red supergiant stars in clusters
Clear identifications of Galactic young stellar clusters farther than a few
kpc from the Sun are rare, despite the large number of candidate clusters. We
aim to improve the selection of candidate clusters rich in massive stars with a
multiwavelength analysis of photometric Galactic data that range from optical
to mid-infrared wavelengths. We present a photometric and spectroscopic
analysis of five candidate stellar clusters, which were selected as
overdensities with bright stars (Ks < 7 mag) in GLIMPSE and 2MASS images. A
total of 48 infrared spectra were obtained. The combination of photometry and
spectroscopy yielded six new red supergiant stars with masses from 10 Msun to
15 Msun. Two red supergiants are located at Galactic coordinates
(l,b)=(16.7deg,-0.63deg) and at a distance of about ~3.9 kpc; four other red
supergiants are members of a cluster at Galactic coordinates
(l,b)=(49.3deg,+0.72deg) and at a distance of ~7.0 kpc. Spectroscopic analysis
of the brightest stars of detected overdensities and studies of interstellar
extinction along their line of sights are fundamental to distinguish regions of
low extinction from actual stellar clusters. The census of young star clusters
containing red supergiants is incomplete; in the existing all-sky near-infrared
surveys, they can be identified as overdensities of bright stars with infrared
color-magnitude diagrams characterized by gaps.Comment: 16 pages, 10 figures, accepted to A&A 201
An Optical Study of Stellar and Interstellar Environments of Seven Luminous and Ultraluminous X-Ray Sources
We have studied the stellar and interstellar environments of two luminous
X-ray sources and five ultraluminous X-ray sources (ULXs) in order to gain
insight into their nature. Archival Hubble Space Telescope images were used to
identify the optical counterparts of the ULXs Ho IX X-1 and NGC 1313 X-2, and
to make photometric measurements of the local stellar populations of these and
the luminous source IC 10 X-1. We obtained high-dispersion spectroscopic
observations of the nebulae around these seven sources to search for He II
lambda-4686 emission and to estimate the expansion velocities and kinetic
energies of these nebulae. Our observations did not detect nebular He II
emission from any source, with the exception of LMC X-1; this is either because
we missed the He III regions or because the nebulae are too diffuse to produce
He II surface brightnesses that lie within our detection limit. We compare the
observed ionization and kinematics of the supershells around the ULXs Ho IX X-1
and NGC 1313 X-2 with the energy feedback expected from the underlying stellar
population to assess whether additional energy contributions from the ULXs are
needed. In both cases, we find insufficient UV fluxes or mechanical energies
from the stellar population; thus these ULXs may be partially responsible for
the ionization and energetics of their supershells. All seven sources we
studied are in young stellar environments and six of them have optical
counterparts with masses >~7 M_sun; thus, these sources are most likely
high-mass X-ray binaries.Comment: 30 pages, 9 figures. Numerous minor revisions, primarily to more
accurately cite earlier work by Pakull and Mirioni, and to correct
typographical errors. Removed a misleading sentence in the Introduction (re:
X-ray photoionization by ULXs). Accepted for publication in The Astrophysical
Journal. Figures have been reduced in resolution for space requirements;
full-resolution figures may be requested by email to [email protected]
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