11 research outputs found
Gas physical conditions and kinematics of the giant outflow Ou4
Full text linkOu4 is a recently discovered bipolar outflow with a projected size of more
than one degree in the plane of the sky. It is apparently centred on the young
stellar cluster -whose most massive representative is the triple system HR8119-
inside the HII region Sh 2-129. The driving source, the nature, and the
distance of Ou4 are not known. Deep narrow-band imagery of the whole nebula at
arcsec resolution was obtained to study its morphology. Long-slit spectroscopy
of the tips of the bipolar lobes was secured to determine the gas ionization
mechanism, physical conditions, and line-of-sight velocities. An estimate of
the proper motions at the tip of the south lobe using archival images is
attempted. The existing multi-wavelength data for Sh 2-129 and HR 8119 are also
comprehensively reviewed. The morphology of Ou4, its emission-line spatial
distribution, line flux ratios, and the kinematic modelling adopting a
bow-shock parabolic geometry, illustrate the expansion of a shock-excited fast
collimated outflow. The radial velocities and reddening are consistent with
those of Sh 2-129 and HR 8119. The improved determination of the distance to
HR8119 (composed of two B0 V and one B0.5 V stars) and Sh 2-129 is 712 pc. We
identify in WISE images a 5 arcmin-radius (1 pc at the distance above) bubble
of emission at 22 micron emitted by hot (107 K) dust, located inside the
central part of Ou4 and corresponding to several [O III] features of Ou4. The
apparent position and the properties studied in this work are consistent with
the hypothesis that Ou4 is located inside the Sh 2-129 HII region, suggesting
that it was launched some 90 000 yrs ago by HR8119. The outflow total kinetic
energy is estimated to be ~4e47~ergs. However, the alternate possibility that
Ou4 is a bipolar planetary nebula, or the result of an eruptive event on a
massive AGB or post-AGB star not yet identified, cannot be ruled out.Comment: Accepted for publication in Astronomy and Astrophysics. Also
available at http://hal.archives-ouvertes.fr/hal-0102228
On the derivation of radial velocities of SB2 components: a "CCF vs TODCOR" comparison
Full text linkThe radial velocity (RV) of a single star is easily obtained from
cross-correlation of the spectrum with a template, but the treatment of
double-lined spectroscopic binaries (SB2s) is more difficult. Two different
approaches were applied to a set of SB2s: the fit of the cross-correlation
function with two normal distributions, and the cross-correlation with two
templates, derived with the TODCOR code. It appears that the minimum masses
obtained through the two methods are sometimes rather different, although their
estimated uncertainties are roughly equal. Moreover, both methods induce a
shift in the zero point of the secondary RVs, but it is less pronounced for
TODCOR. All-in-all the comparison between the two methods is in favour of
TODCOR.Comment: 5 pages, 4 figures, SF2A Conference 201
Search for young stars among ROSAT All-Sky Survey X-ray sources in and around the R CrA dark cloud
Get PDFWe present the ROSAT All-Sky Survey data in a 126 deg^2 area in and around
the CrA star forming region. With low-resolution spectroscopy of unidentified
ROSAT sources we could find 19 new pre-main sequence stars, two of which are
classical T Tauri stars, the others being weak-lined. The spectral types of
these new T Tauri stars range from F7 to M6. The two new classical T Tauri
stars are located towards two small cloud-lets outside of the main CrA cloud.
They appear to be ~10 Myrs old, by comparing their location in the H-R diagram
with isochrones for an assumed distance of 130 pc, the distance of the main CrA
dark cloud. The new off-cloud weak-line T Tauri stars may have formed in
similar cloud-lets, which have dispersed recently. High-resolution spectra of
our new T Tauri stars show that they have significantly more lithium absorption
than zero-age main-sequence stars of the same spectral type, so that they are
indeed young. From those spectra we also obtained rotational and radial
velocities. For some stars we found the proper motion in published catalogs.
The direction and velocity of the 3D space motion - south relative to the
galatic plane - of the CrA T Tauri stars is consistent with the dark cloud
being formed originally by a high-velocity cloud impact onto the galactic
plane, which triggered the star formation in CrA. We also present VRIJHK
photometry for most of the new T Tauri stars to derive their luminosities,
ages, and masses.Comment: A&A Suppl. in pres
Masses of the components of SB2 binaries observed with Gaia. I. Selection of the sample and mass ratios of 20 new SB2s discovered with Sophie
Full text linkIn anticipation of the Gaia astrometric mission, a large sample of
spectroscopic binaries is being observed since 2010 with the Sophie
spectrograph at the Haute--Provence Observatory. Our aim is to derive the
orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy
sufficient to finally obtain the masses of the components with relative errors
as small as 1% when the astrometric measurements of Gaia are taken into
account. Simultaneously, the luminosities of the components in the Gaia
photometric band G will also be obtained. Our observation program started with
200 SBs, including 152 systems that were only known as single-lined. Thanks to
the high efficiency of the Sophie spectrograph, an additional component was
found for 25 SBs. After rejection of 5 multiple systems, 20 new SB2s were
retained, including 8 binaries with evolved primary, and their mass ratios were
derived. Our final sample contains 68 SB2s, including 2 late-type giants and 10
other evolved stars.Comment: 8 pages, 3 figures, accepted for publication in MNRA
The X-ray source content of the XMM-Newton Galactic plane survey
Get PDFWe report the results of an optical campaign carried out by the XMM-Newton Survey Science Centre with the specific goal of identifying the brightest X-ray sources in the XMM-Newton Galactic plane survey. In addition to photometric and spectroscopic observations obtained at the ESO-VLT and ESO-3.6 m, we used cross-correlations with the 2XMMi, USNO-B1.0, MASS, and GLIMPSE catalogues to advance the identification process. Active coronae account for 16 of the 30 positively or tentatively identified X-ray sources and exhibit the softest X-ray spectra. Many of the identified hard X-ray sources are associated with massive stars, possible members of binary systems and emitting at intermediate X-ray luminosities of 1032−34 erg s−1. Among these are (i) a very absorbed, likely hyper-luminous star with X-ray/optical spectra and luminosities comparable to those of η Carina; (ii) a new X-rayselected WN8 Wolf-Rayet star in which most of the X-ray emission probably arises from wind collision in a binary; (iii) a new Be/X-ray star belonging to the growing class of γ-Cas analogues; and (iv) a possible supergiant X-ray binary of the kind discovered recently by INTEGRAL. One of the sources, XGPS-25, has a counterpart of moderate optical luminosity that exhibits HeII λ4686 and Bowen CIII-NIII emission lines, suggesting that this may be a quiescent or X-ray shielded low mass X-ray binary, although its X-ray properties might also be consistent with a rare kind of cataclysmic variable (CV). We also report the discovery of three new CVs, one of which is a likely magnetic system displaying strong X-ray variability. The soft (0.4–2.0 keV) band log N(>S )−log S curve is completely dominated by active stars in the flux range of 1 × 10−13 to 1 × 10−14 erg cm−2 s−1. Several active coronae are also detected above 2 keV suggesting that the population of RS CVn binaries contributes significantly to the hard X-ray source population. In total, we are able to identify a large fraction of the hard (2–10 keV) X-ray sources in the flux range of 1 × 10−12 to 1 × 10−13 erg cm−2 s−1 with Galactic objects at a rate consistent with what is expected for the Galactic contribution alone.We thank an anonymous referee for useful comments which helped to improve the quality of this paper. We are grateful to O. Herent for carrying out some of the observations presented in this work. This work has been supported in part by the DLR (Deutsches Zentrum für Luftund Raumfahrt) under grants 50 OX 0201 and 50 OX 0801. I.N. is supported by the Spanish Ministerio de Ciencia e Innovación under grants AYA2008-06166-C03-03 and CSD2006-70. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The DENIS project has been partly funded by the SCIENCE and the HCM plans of the European Commission under grants CT920791 and CT940627. It is supported by INSU, MEN and CNRS in France, by the State of Baden-Württemberg in Germany, by DGICYT in Spain, by CNR in Italy, by FFwFBWF in Austria, by
FAPESP in Brazil, by OTKA grants F-4239 and F-013990 in Hungary, and by the ESO C&EE grant A-04-046. Jean Claude Renault from IAP was the Project manager. Observations were carried out thanks to the contribution of numerous students and young scientists from all involved institutes, under the supervision of P. Fouqué, survey astronomer resident in Chile. The WHT is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de AstrofÃsica de Canarias. The observation
presented here was taken as part of the ING service programme (proposal SW2005A06). This research has made use of Aladin, of the VizieR catalogue access tool and of Simbad at CDS, Strasbourg, France
New SB2 orbital elements for accurate masses with Gaia: HD 9312, HD 9313 and HD 183255
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A new method based on Markov chains for deriving SB2 orbits directly from their spectra
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