106 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
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 and X-ray Examination of Two Radio Supernova Remnant Candidates in 30 Doradus
The giant HII region 30 Doradus is known for its violent internal motions and
bright diffuse X-ray emission, suggesting the existence of supernova remnants
(SNRs), but no nonthermal radio emission has been detected. Recently, Lazendic
et al. compared the H-alpha/H-beta and radio/H-alpha ratios and suggested two
small radio sources to be nonthermal and thus SNR candidates; however, no
optical or X-ray counterparts were detected. We have used high-resolution
optical images and high-dispersion spectra to examine the morphological,
spectral, and kinematic properties of these two SNR candidates, and still find
no optical evidence supporting their identification as SNRs. We have also
determined the X-ray luminosities of these SNR candidates, and find them 1-3
orders of magnitude lower than those commonly seen in young SNRs. High
extinction can obscure optical and X-ray signatures of an SNR, but would
prohibit the use of a high radio/H-alpha ratio to identify nonthermal radio
emission. We suggest that the SNR candidate MCRX J053831.8-690620 is associated
with a young star forming region; while the radio emission originates from the
obscured star forming region, the observed optical emission is dominated by the
foreground. We suggest that the SNR candidate MCRX J053838.8-690730 is
associated with a dust/molecular cloud, which obscures some optical emission
but not the radio emission.Comment: 13 pages, 2 figures, accepted for publication in the ApJ, Nov 10,
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