50,988 research outputs found
An X-ray and Infrared Survey of the Lynds 1228 Cloud Core
The nearby Lynds 1228 (L1228) dark cloud at a distance of ~200 pc is known to
harbor several young stars including the driving sources of the giant HH 199
and HH 200 Herbig-Haro outflows. L1228 has been previously studied at optical,
infrared, and radio wavelengths but not in X-rays. We present results of a
sensitive 37 ks Chandra ACIS-I X-ray observation of the L1228 core region.
Chandra detected 60 X-ray sources, most of which are faint (<40 counts) and
non-variable. Infrared counterparts were identified for 53 of the 60 X-ray
sources using archival data from 2MASS, Spitzer, and WISE. Object classes were
assigned using mid-IR colors for those objects with complete photometry, most
of which were found to have colors consistent with extragalactic background
sources. Seven young stellar object (YSO) candidates were identified including
the class I protostar HH 200-IRS which was detected as a faint hard X-ray
source. No X-ray emission was detected from the luminous protostar HH 199-IRS.
We summarize the X-ray and infrared properties of the detected sources and
provide IR spectral energy distribution modeling of high-interest objects
including the protostars driving the HH outflows.Comment: 38 pages, 7 tables, 8 figures; to appear in A
Modeling the HD32297 Debris Disk with Far-IR Herschel Data
HD32297 is a young A-star (~30 Myr) 112 pc away with a bright edge-on debris
disk that has been resolved in scattered light. We observed the HD32297 debris
disk in the far-infrared and sub-millimeter with the Herschel Space Observatory
PACS and SPIRE instruments, populating the spectral energy distribution (SED)
from 63 to 500{\mu}m. We aimed to determine the composition of dust grains in
the HD32297 disk through SED modeling, using geometrical constraints from the
resolved imaging to break degeneracies inherent in SED modeling. We found the
best fitting SED model has 2 components: an outer ring centered around 110 AU,
seen in the scattered light images, and an inner disk near the habitable zone
of the star. The outer disk appears to be composed of grains > 2{\mu}m
consisting of silicates, carbonaceous material, and water ice with an abundance
ratio of 1:2:3 respectively and 90% porosity. These grains appear consistent
with cometary grains, implying the underlying planetesimal population is
dominated by comet-like bodies. We also discuss the 3.7{\sigma} detection of [C
II] emission at 158{\mu}m with the Herschel PACS Spectrometer, making HD32297
one of only a handful of debris disks with circumstellar gas detected.Comment: 11 pages, 4 figures, accepted for publication in The Astrophysical
Journa
Discovery of Resolved Debris Disk Around HD 131835
We report the discovery of the resolved disk around HD 131835 and present the
analysis and modeling of its thermal emission. HD 131835 is a ~15 Myr A2 star
in the Scorpius-Centaurus OB association at a distance of 122.7 +16.2 -12.8
parsec. The extended disk has been detected to ~1.5" (200 AU) at 11.7 {\mu}m
and 18.3 {\mu}m with T-ReCS on Gemini South. The disk is inclined at an angle
of ~75{\deg} with the position angle of ~61{\deg}. The flux of HD 131835 system
is 49.3+-7.6 mJy and 84+-45 mJy at 11.7 {\mu}m and 18.3 {\mu}m respectively. A
model with three grain populations gives a satisfactory fit to both the
spectral energy distribution and the images simultaneously. This best-fit model
is composed of a hot continuous power-law disk and two rings. We characterized
the grain temperature profile and found that the grains in all three
populations are emitting at temperatures higher than blackbodies. In
particular, the grains in the continuous disk are unusually warm; even when
considering small graphite particles as the composition.Comment: 11 pages, 5 figures, Accepted for Publication in Ap
Chandra Reveals Heavy Obscuration and Circumnuclear Star Formation in Seyfert 2 Galaxy NGC 4968
We present the Chandra imaging and spectral analysis of NGC 4968, a nearby (z
= 0.00986) Seyfert 2 galaxy. We discover extended (1 kpc) X-ray emission
in the soft band (0.5 - 2 keV) that is neither coincident with the narrow line
region nor the extended radio emission. Based on spectral modeling, it is
linked to on-going star formation (2.6-4 M_{\sun} yr). The soft
emission at circumnuclear scales (inner 400 pc) originates from hot gas,
with kT 0.7 keV, while the most extended thermal emission is cooler (kT
0.3 keV). We refine previous measurements of the extreme Fe K
equivalent width in this source (EW = 2.5 keV), which suggests
the central engine is completely embedded within Compton-thick levels of
obscuration. Using physically motivated models fit to the Chandra spectrum, we
derive a Compton-thick column density (
cm) and an intrinsic hard (2-10 keV) X-ray luminosity of
3-8 erg s (depending on the presumed geometry of
the obscurer), which is over two orders of magnitude larger than that observed.
The large Fe K EW suggests a spherical covering geometry, which could
be confirmed with X-ray measurements above 10 keV. NGC 4968 is similar to other
active galaxies that exhibit extreme Fe K EWs (i.e., 2 keV) in that
they also contain ongoing star formation. This work supports the idea that gas
associated with nuclear star formation may increase the covering factor of the
enshrouding gas and play a role in obscuring AGN.Comment: 11 pages, 8 figures, 4 tables. Accepted for publication in Ap
Asteroid Models from Multiple Data Sources
In the past decade, hundreds of asteroid shape models have been derived using
the lightcurve inversion method. At the same time, a new framework of 3-D shape
modeling based on the combined analysis of widely different data sources such
as optical lightcurves, disk-resolved images, stellar occultation timings,
mid-infrared thermal radiometry, optical interferometry, and radar
delay-Doppler data, has been developed. This multi-data approach allows the
determination of most of the physical and surface properties of asteroids in a
single, coherent inversion, with spectacular results. We review the main
results of asteroid lightcurve inversion and also recent advances in multi-data
modeling. We show that models based on remote sensing data were confirmed by
spacecraft encounters with asteroids, and we discuss how the multiplication of
highly detailed 3-D models will help to refine our general knowledge of the
asteroid population. The physical and surface properties of asteroids, i.e.,
their spin, 3-D shape, density, thermal inertia, surface roughness, are among
the least known of all asteroid properties. Apart for the albedo and diameter,
we have access to the whole picture for only a few hundreds of asteroids. These
quantities are nevertheless very important to understand as they affect the
non-gravitational Yarkovsky effect responsible for meteorite delivery to Earth,
or the bulk composition and internal structure of asteroids.Comment: chapter that will appear in a Space Science Series book Asteroids I
RCW 86: A Type Ia Supernova in a Wind-Blown Bubble
We report results from a multi-wavelength analysis of the Galactic SNR RCW
86, the proposed remnant of the supernova of 185 A.D. We report new infrared
observations from {\it Spitzer} and {\it WISE}, where the entire shell is
detected at 24 and 22 m. We fit the infrared flux ratios with models of
collisionally heated ambient dust, finding post-shock gas densities in the
non-radiative shocks of 2.4 and 2.0 cm in the SW and NW portions of the
remnant, respectively. The Balmer-dominated shocks around the periphery of the
shell, large amount of iron in the X-ray emitting ejecta, and lack of a compact
remnant support a Type Ia origin for this remnant. From hydrodynamic
simulations, the observed characteristics of RCW 86 are successfully reproduced
by an off-center explosion in a low-density cavity carved by the progenitor
system. This would make RCW 86 the first known case of a Type Ia supernova in a
wind-blown bubble. The fast shocks ( km s) observed in the NE
are propagating in the low-density bubble, where the shock is just beginning to
encounter the shell, while the slower shocks elsewhere have already encountered
the bubble wall. The diffuse nature of the synchrotron emission in the SW and
NW is due to electrons that were accelerated early in the lifetime of the
remnant, when the shock was still in the bubble. Electrons in a bubble could
produce gamma-rays by inverse-Compton scattering. The wind-blown bubble
scenario requires a single-degenerate progenitor, which should leave behind a
companion star.Comment: Accepted for publication in ApJ. 50 pages, 9 figure
- …