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Register a new userThe X-ray emission from Young Stellar Objects in the rho Ophiuchi cloud core as seen by XMM-Newton
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We observed the main core F of the rho Ophiuchi cloud, an active star-forming region located at ~140 pc, using XMM-Newton with an exposure of 33 ks. We detect 87 X-ray sources within the 30 diameter field-of-view of the it EPIC imaging detector array. We cross-correlate the positions of XMM-Newton X-ray sources with previous X-ray and infrared (IR) catalogs: 25 previously unknown X-ray sources are found from our observation; 43 X-ray sources are detected by both XMM-Newton and Chandra; 68 XMM-Newton X-ray sources have 2MASS near-IR counterparts. We show that XMM-Newton and Chandra have comparable sensitivity for point source detection when the exposure time is set to ~30 ks for both. We detect X-ray emission from 7 Class I sources, 26 Class II sources, and 17 Class III sources. The X-ray detection rate of Class I sources is very high (64 %), which is consistent with previous Chandra observations in this area. We propose that 15 X-ray sources are new class III candidates, which doubles the number of known Class III sources, and helps to complete the census of YSOs in this area. We also detect X-ray emission from two young bona fide brown dwarfs, GY310 and GY141, out of three known in the field of view. GY141 appears brighter by nearly two orders of magnitude than in the Chandra observation. We extract X-ray light curves and spectra from these YSOs, and find some of them showed weak X-ray flares. We observed an X-ray flare from the bona fide brown dwarf GY310. We find as in the previous Chandra observation of this region that Class I sources tend to have higher temperatures and heavier X-ray absorptions than Class II and III sources.
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The results of a near-infrared (J H K LP) imaging linear polarimetry survey of 20 young stellar objects (YSOs) in rho Ophiuchi are presented. The majority of the sources are unresolved, with K-band polarizations, P_K < 6 per cent. Several objects are associated with extended reflection nebulae. These objects have centrosymmetric vector patterns with polarization discs over their cores; maximum polarizations of P_K > 20 per cent are seen over their envelopes. Correlations are observed between the degree of core polarization and the evolutionary status inferred from the spectral energy distribution. K-band core polarizations >6 per cent are only observed in Class I YSOs. A 3D Monte Carlo model with oblate grains aligned with a magnetic field is used to investigate the flux distributions and polarization structures of three of the rho Oph YSOs with extended nebulae. A rho proportional to r^(-1.5) power law for the density is applied throughout the envelopes. The large-scale centrosymmetric polarization structures are due to scattering. However, the polarization structure in the bright core of the nebula appears to require dichroic extinction by aligned non-spherical dust grains. The position angle indicates a toroidal magnetic field in the inner part of the envelope. Since the measured polarizations attributed to dichroic extinction are usually <10 per cent, the grains must either be nearly spherical or very weakly aligned. The higher polarizations observed in the outer parts of the reflection nebulae require that the dust grains responsible for scattering have maximum grain sizes <=1.05 microns.
Star formation in molecular clouds can be triggered by the dynamical action of winds from massive stars. Furthermore, X-ray and UV fluxes from massive stars can influence the life time of surrounding circumstellar disks. We present the results of a 53 ks XMM-Newton observation centered on the Rho Ophiuchi A+B binary system. Rho Ophiiuchi lies in the center of a ring of dust, likely formed by the action of its winds. This region is different from the dense core of the cloud (L1688 Core F) where star formation is at work. X-rays are detected from Rho Ophiuchi as well as a group of surrounding X-ray sources. We detected 89 X-ray sources, 47 of them have at least one counterpart in 2MASS + All-WISE catalogs. Based on IR and X-ray properties, we can distinguish between young stellar objects (YSOs) belonging to the cloud and background objects. Among the cloud members, we detect 3 debris disk objects and 22 disk-less / Class III young stars. We show that these stars have ages in $5-10$ Myr, and are significantly older than the YSOs in L1688. We speculate that they are the result of an early burst of star formation in the cloud. An X-ray energy of $ge5times10^{44}$ ergs has been injected into the surrounding medium during the past $5$ Myr, we discuss the effects of such energy budget in relation to the cloud properties and dynamics.
Molecular oxygen, O2 has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission. The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core rho Oph A was observed with Odin for 34 days during several observing runs. We detect a spectral line at v(LSR) = 3.5 km/s with dv(FWHM) = 1.5 km/s, parameters which are also common to other species associated with rho Ohp A. This feature is identified as the O2 (N_J = 1_1 - 1_0) transition at 118 750.343 MHz. The abundance of molecular oxygen, relative to H2,, is 5E-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.
GX 339--4 is a well-known microquasar. In this contribution we show the obtained results with the INTEGRAL and XMM-Newton observatories of the outburst undertaken on 2007. The observations cover spectral evolution from the hard, soft intermediate states to the high/soft state. Spectral hardening correlated with the appearance of an skewed Fe line is detected during one of the observations during the soft intermediate state. In all spectral states joint XMM/EPIC-pn, JEM-X, ISGRI and SPI data were fit with the hybrid thermal/non-thermal Comptonization model (EQPAIR). With this model a non-thermal component seems to be required by the data in all the observations. Our results imply evolution in the coronal properties, the most important one being the transition from a compact corona in the first observation to the disappearance of coronal material in the second and re-appearance in the third. We discuss the results obtained in the context of possible physical scenarios for the origin and geometry of the corona and its relation to black hole states.
We present the results of two XMM-Newton observations of Jupiter carried out in 2003 for 100 and 250 ks (or 3 and 7 planet rotations) respectively. X-ray images from the EPIC CCD cameras show prominent emission from the auroral regions in the 0.2 - 2.0 keV band: the spectra are well modelled by a combination of emission lines, including most prominently those of highly ionised oxygen (OVII and OVIII). In addition, and for the first time, XMM-Newton reveals the presence in both aurorae of a higher energy component (3 - 7 keV) which is well described by an electron bremsstrahlung spectrum. This component is found to be variable in flux and spectral shape during the Nov. 2003 observation, which corresponded to an extended period of intense solar activity. Emission from the equatorial regions of Jupiters disk is also observed, with a spectrum consistent with that of solar X-rays scattered in the planets upper atmosphere. Jupiters X-rays are spectrally resolved with the RGS which clearly separates the prominent OVII contribution of the aurorae from the OVIII, FeXVII and MgXI lines, originating in the low-latitude disk regions of the planet.
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