76 research outputs found
XMM-Newton and Chandra observations of G272.2-3.2. Evidence of stellar ejecta in the central region
We aim to study the spatial distribution of the physical and chemical
properties of the X-ray emitting plasma of the supernova remnant G272.2-3.2, in
order to get important constraints on its ionization stage, on the progenitor
supernova explosion, and the age of the remnant. We report combined XMM-Newton
and Chandra images, median photon energy map, silicon and sulfur equivalent
width maps, and a spatially resolved spectral analysis for a set of regions of
the remnant. Complementary radio and H{\alpha} observations, available in the
literature, are also used to study the multi-wavelength connection of all
detected emissions. The X-ray morphology of the remnant displays an overall
structure with an almost circular appearance, a centrally brightened hard
region, with a peculiar elongated hard structure oriented along the
northwest-southeast direction of the central part. The X-ray spectral study of
the regions shows distinct K{\alpha} emission-line features of metal elements,
confirming the thermal origin of the emission. The X-ray spectra are well
represented by an absorbed VNEI thermal plasma model, which produces elevated
abundances of Si, S, and Fe in the circular central region, typical of ejecta
material. The values of abundances found in the central region of the SNR favor
a Type Ia progenitor for this remnant. The outer region shows abundances below
the solar value, as expected if the emission arises from the shocked ISM. The
relatively low ionization timescales suggests non-equilibrium ionization. We
identify the location of the contact discontinuity. Its distance to the outer
shock is higher than expected for expansion in a uniform media, what suggests
that the remnant spent most of its time in a more dense medium.Comment: 9 pages, 7 figures. Accepted for publication in A&
Optical Spectroscopy of X-Mega targets in the Carina Nebula - VI. FO 15: a new O-Type double-lined eclipsing binary
We report the discovery of a new O-type double-lined spectroscopic binary
with a short orbital period of 1.4 days. We find the primary component of this
binary, FO 15, to have an approximate spectral type O5.5Vz, i.e. a
Zero-Age-Main-Sequence star. The secondary appears to be of spectral type
O9.5V. We have performed a numerical model fit to the public ASAS photometry,
which shows that FO 15 is also an eclipsing binary. We find an orbital
inclination of ~ 80 deg. From a simultaneous light-curve and radial velocity
solution we find the masses and radii of the two components to be 30 +/- 1 and
16 +/- 1 solar masses and 7.5 +/- 0.5 and 5.3 +/- 0.5 solar radii. These radii,
and hence also the luminosities, are smaller than those of normal O-type stars,
but similar to recently born ZAMS O-type stars. The absolute magnitudes derived
from our analysis locate FO 15 at the same distance as Eta Carinae. From
Chandra and XMM X-ray images we also find that there are two close X-ray
sources, one coincident with FO 15 and another one without optical counterpart.
This latter seems to be a highly variable source, presumably due to a
pre-main-sequence stellar neighbour of FO 15.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRAS.
Higher resolution version available at
http://lilen.fcaglp.unlp.edu.ar/papers2006.htm
Evidence of non-thermal X-ray emission from HH 80
Protostellar jets appear at all stages of star formation when the accretion
process is still at work. Jets travel at velocities of hundreds of km/s,
creating strong shocks when interacting with interstellar medium. Several cases
of jets have been detected in X-rays, typically showing soft emission. For the
first time, we report evidence of hard X-ray emission possibly related to
non-thermal processes not explained by previous models of the post-shock
emission predicted in the jet/ambient interaction scenario. HH 80 is located at
the south head of the jet associated to the massive protostar IRAS 18162-2048.
It shows soft and hard X-ray emission in regions that are spatially separated,
with the soft X-ray emission region situated behind the region of hard X-ray
emission. We propose a scenario for HH 80 where soft X-ray emission is
associated to thermal processes from the interaction of the jet with denser
ambient matter and the hard X-ray emission is produced by synchrotron radiation
at the front shock.Comment: Accepted for publication in ApJ
X-ray structures from outflowing Young Stellar Objects interacting with the Interstellar Medium
T Tauri stars as -ray source in the Rho Ophiuchi region
More than 30 % of -ray sources detected in the last source catalog of
the Fermi satellite have no observational counterpart at other frequencies. A
significant fraction of these sources is positionally in agreement with
star-forming regions dominated by associations of T Tauri stars. Rho Ophiuchi,
which is one of the closest star-forming regions, matches the unidentified
Fermi source 4FGL J1625.3-2338. In this work we modeled the spectral energy
distribution considering some dominant radiative processes in T Tauri stars.
Accounting for a total of 22 Class III T Tauri stars in the region, integrated
-ray luminosity in the 100 MeV to 100 GeV energy range is consistent
with the observed in the catalog for the 4FGL J1625.3-2338 source.Comment: Accepted for publication on the Bulletin of the Argentinian
Association of Astronomy. 3 pages, 3 figure
AE Aurigae: first detection of non-thermal X-ray emission from a bow shock produced by a runaway star
Runaway stars produce shocks when passing through interstellar medium at
supersonic velocities. Bow shocks have been detected in the mid-infrared for
several high-mass runaway stars and in radio waves for one star. Theoretical
models predict the production of high-energy photons by non-thermal radiative
processes in a number sufficiently large to be detected in X-rays. To date, no
stellar bow shock has been detected at such energies. We present the first
detection of X-ray emission from a bow shock produced by a runaway star. The
star is AE Aur, which was likely expelled from its birthplace by the encounter
of two massive binary systems and now is passing through the dense nebula IC
405. The X-ray emission from the bow shock is detected at 30" to the northeast
of the star, coinciding with an enhancement in the density of the nebula. From
the analysis of the observed X-ray spectrum of the source and our theoretical
emission model, we confirm that the X-ray emission is produced mainly by
inverse Compton upscattering of infrared photons from dust in the shock front.Comment: Accepted for publication in the Astrophysical Journal with number
ApJ, 757, L6. Four figure
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