569 research outputs found
HDE 245059: A Weak-Lined T Tauri Binary Revealed by Chandra and Keck
We present the Chandra High Energy Transmission Grating Spectrometer (HETGS)
and Keck observations of HDE 245059, a young weak-lined T Tauri star (WTTS),
member of the pre-main sequence group in the Lambda Orionis Cluster. Our high
spatial resolution, near-infrared observations with Keck reveal that HDE 245059
a binary separated by 0.87". Based on this new information we have obtained an
estimate of the masses of the binary components; 3M_{sun} and 2.5M_{sun} for
the north and south components, respectively. We have estimated the age of the
system to be ~2-3 Myr. We detect both components of the binary in the zeroth
order Chandra image and in the grating spectra. Our fits to the spectrum of the
binary have shown that the emission is dominated by a plasma between 8 and 15
MK, a soft component at 4 MK and a hard component at 50 MK are also detected.
The value of the hydrogen column density was low, 8 x 10^{19} cm^{-2}, likely
due to the clearing of the inner region of the Lambda Orionis cloud. The
abundance pattern shows an inverse First Ionization Potential (FIP) effect for
all elements from O to Fe, the only exception being Ca. A 3-T model was fitted
to the individual zeroth order spectra using the abundances derived for the
binary. We have also obtained several lines fluxes from the grating spectra.
The fits to the triplets show no evidence of high densities. We conclude that
the X-ray properties of the weak-lined T Tau binary HDE 245059 are similar to
those generally observed in other weak-lined T Tau stars. Although its
accretion history may have been affected by the clearing of the interstellar
material around Lambda Ori, its coronal properties appears not to have been
strongly modified.Comment: 12 pages, 10 figures Accepted for publication in Ap
A Study of the Coronal Plasma in RS CVn binary systems
XMM-Newton has been performing comprehensive studies of X-ray bright RS CVn
binaries in its Calibration and Guaranteed Time programs. We present results
from ongoing investigations in the context of a systematic study of coronal
emission from RS CVns. We concentrate in this paper on coronal abundances and
investigate the abundance pattern in RS CVn binaries as a function of activity
and average temperature. A transition from an Inverse First Ionization
Potential (FIP) effect towards an absence of a clear trend is found in
intermediately active RS CVn systems. This scheme corresponds well into the
long-term evolution from an IFIP to a FIP effect found in solar analogs. We
further study variations in the elemental abundances during a large flare.Comment: to appear in The Twelfth Cool Stars, Stellar Systems and the Sun,
eds. A. Brown, T.R. Ayres, G.M. Harper, (Boulder: Univ. of Colorado), in
pres
Infrared and sub-mm observations of outbursting young stars with Herschel and Spitzer
Episodic accretion plays an important role in the evolution of young stars.
Although it has been under investigation for a long time, the origin of such
episodic accretion events is not yet understood. We investigate the dust and
gas emission of a sample of young outbursting sources in the infrared to get a
better understanding of their properties and circumstellar material, and we use
the results in a further work to model the objects. We used Herschel data, from
our PI program of 12 objects and complemented with archival observations to
obtain the spectral energy distributions (SEDs) and spectra of our targets. We
report here the main characteristics of our sample, focussing on the SED
properties and on the gas emission lines detected in the PACS and SPIRE
spectra. The SEDs of our sample show the diversity of the outbursting sources,
with several targets showing strong emission in the far-infrared from the
embedded objects. Most of our targets reside in a complex environment, which we
discuss in detail. We detected several atomic and molecular lines, in
particular rotational CO emission from several transitions from J=38-37 to
J=4-3. We constructed rotational diagrams for the CO lines, and derived in
three domains of assumed local thermodynamic equilibrium (LTE) temperatures and
column densities, ranging mainly between 0-100 K and 400-500K. We confirm
correlation in our sample between intense CO emission and the column
density of the warm domain of CO, N(warm). We notice a strong increase in
luminosity of HH 381 IRS and a weaker increase for PP 13 S, which shows the
beginning of an outburst.Comment: 23 pages, 17 figures, A&A accepte
A Preliminary Seismic Analysis of 51 Peg: Large and Small Spacings from Standard Models
We present a preliminary theoretical seismic study of the astronomically
famous star 51 Peg. This is done by first performing a detailed analysis within
the Hertzsprung-Russell diagram (HRD). Using the Yale stellar evolution code
(YREC), a grid of stellar evolutionary tracks has been constructed for the
masses 1.00 M_sun, 1.05 M_sun and 1.10 M_sun, in the metallicity range
Z=0.024-0.044, and for values of the Galactic helium enrichment ratio DY/DZ in
the range 0-2.5. Along these evolutionary tracks, we select 75 stellar model
candidates that fall within the 51 Peg observational error box in the HRD (all
turn out to have masses of 1.05 M_sun and 1.10 M_sun. The corresponding
allowable age range for these models, which depends sensitively on the
parameters of the model, is relatively large and is ~2.5 - 5.5 Gyr. For each of
the 75 models, a non-radial pulsation analysis is carried out, and the large
and small frequency spacings are calculated. The results show that just
measuring the large and small frequency spacings will greatly reduce the
present uncertainties in the derived physical parameters and in the age of 51
Peg. Finally we discuss briefly refinements in the physics of the models and in
the method of analysis which will have to be included in future models to make
the best of the precise frequency determinations expected from space
observations.Comment: 22 pages, 5 figures, 3 tables. Accepted for publicaton by Ap
First Light Measurements with the XMM-Newton Reflection Grating Spectrometers: Evidence for an Inverse First Ionisation Potential Effect and Anomalous Ne A bundance in the Coronae of HR 1099
The RS CVn binary system HR 1099 was extensively observed by the XMM-Newton
observatory in February 2000 as its first-light target. A total of 570 ks of
exposure time was accumulated with the Reflection Grating Spectrometers (RGS).
The integrated X-ray spectrum between 5-35 Angstrom is of unprecedented quality
and shows numerous features attributed to transitions of the elements C, N, O,
Ne, Mg, Si, S, Fe, and Ni. We perform an in-depth study of the elemental
composition of the average corona of this system, and find that the elemental
abundances strongly depend on the first ionisation potential (FIP) of the
elements. But different from the solar coronal case, we find an inverse FIP
effect, i.e., the abundances (relative to oxygen) increase with increasing FIP.
Possible scenarios, e.g., selective enrichment due to Ne-rich flare-like
events, are discussed.Comment: 5 pages, 4 figures. Accepted by A&A Letters, XMM issu
X-Ray Evidence for Flare Density Variations and Continual Chromospheric Evaporation in Proxima Centauri
Using the XMM-Newton X-ray observatory to monitor the nearest star to the
Sun, Proxima Centauri, we recorded the weakest X-ray flares on a magnetically
active star ever observed. Correlated X-ray and optical variability provide
strong support for coronal energy and mass supply by a nearly continuous
sequence of rapid explosive energy releases. Variable emission line fluxes were
observed in the He-like triplets of OVII and NeIX during a giant flare. They
give direct X-ray evidence for density variations, implying densities between
2x10^{10} - 4x10^{11} cm^{-3} and providing estimates of the mass and the
volume of the line-emitting plasma. We discuss the data in the context of the
chromospheric evaporation scenario.Comment: 10 pages, 2 figures, accepted by The Astrophysical Journal, Letters;
improved calculations of radiative loss of cool plasma (toward end of paper
Deuteration and evolution in the massive star formation process: the role of surface chemistry
An ever growing number of observational and theoretical evidence suggests
that the deuterated fraction (column density ratio between a species containing
D and its hydrogenated counterpart, Dfrac) is an evolutionary indicator both in
the low- and the high-mass star formation process. However, the role of surface
chemistry in these studies has not been quantified from an observational point
of view. In order to compare how the deuterated fractions of species formed
only in the gas and partially or uniquely on grain surfaces evolve with time,
we observed rotational transitions of CH3OH, 13CH3OH, CH2DOH, CH3OD at 3 and
1.3~mm, and of NH2D at 3~mm with the IRAM-30m telescope, and the inversion
transitions (1,1) and (2,2) of NH3 with the GBT, towards most of the cores
already observed by Fontani et al.~(2011, 2014) in N2H+, N2D+, HNC, DNC. NH2D
is detected in all but two cores, regardless of the evolutionary stage.
Dfrac(NH3) is on average above 0.1, and does not change significantly from the
earliest to the most evolved phases, although the highest average value is
found in the protostellar phase (~0.3). Few lines of CH2DOH and CH3OD are
clearly detected, and only towards protostellar cores or externally heated
starless cores. This work clearly confirms an expected different evolutionary
trend of the species formed exclusively in the gas (N2D+ and N2H+) and those
formed partially (NH2D and NH3) or totally (CH2DOH and CH3OH) on grain mantles.
The study also reinforces the idea that Dfrac(N2H+) is the best tracer of
massive starless cores, while high values of Dfrac(CH3OH) seem rather good
tracers of the early protostellar phases, at which the evaporation/sputtering
of the grain mantles is most efficient.Comment: 14 pages, 7 figures, 2 Appendice
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