N. Grosso

Chandra Orion Ultradeep Project: Observations and Source Lists

We present a description of the data reduction methods and the derived catalog of more than 1600 X-ray point sources from the exceptionally deep 2003 January Chandra X-Ray Observatory (Chandra) observation of the Orion Nebula Cluster and embedded populations around OMC-1. The observation was obtained with Chandras Advanced CCD Imaging Spectrometer (ACIS) and has been nicknamed the Chandra Orion Ultradeep Project (COUP). With an 838 ks exposure made over a continuous period of 13.2 days, the COUP observation provides the most uniform and comprehensive data set on the X-ray emission of normal stars ever obtained in the history of X-ray astronomy.

The XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST)

(abridged:) The XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST) surveys the most populated ~5 square degrees of the Taurus star formation region, using the XMM-Newton X-ray observatory to study the thermal structure, variability, and long-term evolution of hot plasma, to investigate the magnetic dynamo, and to search for new potential members of the association. Many targets are also studied in the optical, and high-resolution X-ray grating spectroscopy has been obtained for selected bright sources. The X-ray spectra have been coherently analyzed with two different thermal models (2-component thermal model, and a continuous emission measure distribution model). We present overall correlations with fundamental stellar parameters that were derived from the previous literature. A few detections from Chandra observations have been added. The present overview paper introduces the project and provides the basic results from the X-ray analysis of all sources detected in the XEST survey.Comprehensive tables summarize the stellar properties of all targets surveyed. The survey goes deeper than previous X-ray surveys of Taurus by about an order of magnitude and for the first time systematically accesses very faint and strongly absorbed TMC objects. We find a detection rate of 85% and 98% for classical and weak-line T Tau stars (CTTS resp. WTTS), and identify about half of the surveyed protostars and brown dwarfs. Overall, 136 out of 169 surveyed stellar systems are detected. We describe an X-ray luminosity vs. mass correlation, discuss the distribution of X-ray-to-bolometric luminosity ratios, and show evidence for lower X-ray luminosities in CTTS compared to WTTS. Detailed analysis (e.g., variability, rotation-activity relations, influence of accretion on X-rays) will be discussed in a series of accompanying papers.

Determination of the gas-to-dust ratio in nearby dense clouds using X-ray absorption measurements

We present a comparison of the gas and dust properties of the dense interstellar matter in six nearby star forming regions (d 2) than the galactic value, derived using the standard extinction curve (RV = 3:1). This result is consistent with the recent downwards revision of the metallicity of the Sun and stars in the solar vicinity. We find that the Oph dense cloud has the same metallicity than the local ISM when assuming that the galactic gas-to-dust ratio remains unchanged. The dierence between galactic and local values of the gas-to-dust ratio can thus be attributed entirely to a dierence in metallicity.

The Taurus Spitzer Survey: New Candidate Taurus Members Selected Using Sensitive Mid-Infrared Photometry

We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in seven mid- and far-infrared bands with the Spitzer Space Telescope. There are 215 previously identified members of the Taurus star-forming region in our ~44 deg^2 map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that ~20% of the bona fide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided by extensive optical, X-ray, and ultraviolet imaging, and found 148 new candidate members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, three probable new members, and 10 possible new members, an increase of 15%–20% in Taurus members. Of the objects for which we have spectroscopy, seven are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and active galactic nuclei.

Dissecting X-ray-Emitting Gas Around the Center of Our Galaxy

The Galaxy Center in X-rays At the center of our Galaxy there is a black hole 4-million-fold more massive than the Sun. Wang et al. (p. 981; see the Perspective by Schnittman) report x-ray data on the accretion flow around this supermassive black hole, revealing how it interacts with its surroundings. The data rule out the possibility that the quiescent (that is, flare-free) x-rays observed are produced by coronal emission from a population of stars at the center of the Galaxy and also rule out the possibility that there is a pure radiatively inefficient accretion flow with no outflows. X-ray observations of the center of our Galaxy reveal the interplay between the massive black hole there and its surroundings. [Also see Perspective by Schnittman] Most supermassive black holes (SMBHs) are accreting at very low levels and are difficult to distinguish from the galaxy centers where they reside. Our own Galaxy’s SMBH provides an instructive exception, and we present a close-up view of its quiescent x-ray emission based on 3 megaseconds of Chandra observations. Although the x-ray emission is elongated and aligns well with a surrounding disk of massive stars, we can rule out a concentration of low-mass coronally active stars as the origin of the emission on the basis of the lack of predicted iron (Fe) Kα emission. The extremely weak hydrogen (H)–like Fe Kα line further suggests the presence of an outflow from the accretion flow onto the SMBH. These results provide important constraints for models of the prevalent radiatively inefficient accretion state.

Global X-Ray Properties of the Orion Nebula Region

Based on the Chandra Orion Ultradeep Project (COUP) observation, we establish the global X-ray properties of the stellar population associated with the Orion Nebula. Three components contribute roughly equally to the integrated COUP luminosity in the hard (2-8 keV) X-ray band: several OB stars, 822 lightly obscured cool stars in the Orion Nebula Cluster (ONC), and 559 heavily obscured stars. ONC stars 0.5-2?pc from the center show a spatial asymmetry consistent with violent relaxation in the stellar dynamics. The obscured COUP sources concentrate around both OMC-1 molecular cores; these small-scale structures indicate ages t 0.1 Myr. The X-ray luminosity function (XLF) of the lightly obscured sample is roughly lognormal in shape. The obscured population is deficient in lower luminosity stars, perhaps due to localized circumstellar material. Mass-stratified XLFs show that one-third of the Orion Nebula region hard-band emission is produced by the bright O6 star ?1 Ori C and half is produced by lower mass pre-main-sequence stars with masses 0.3 M? < M < 3 M?. Very low mass stars contribute little to the cluster X-ray emission. Using the hard band emission, we show that young stellar clusters like the ONC can be readily detected and resolved with Chandra across the Galactic disk, even in the presence of heavy obscuration. The Orion Nebula sample is a valuable template for studies of distant clusters. For example, the peak of the XLF shape can serve as a standard candle for a new distance measure to distant young stellar clusters, and the presence of a neon emission line complex around 1 keV can serve as a diagnostic for young stars.

XMM-Newton observation of the brightest X-ray flare detected so far from Sgr A

We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from Sgr A* with a duration shorter than one hour (~2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of

MEMBERSHIP OF THE ORION NEBULA POPULATION FROM THE CHANDRA ORION ULTRADEEP PROJECT

\Gamma =2.5 \pm0.3

A CHANDRA/HETGS CENSUS OF X-RAY VARIABILITY FROM Sgr A* DURING 2012

, and a peak 2–10 keV luminosity of 3.6

CHANDRA/HETGS OBSERVATIONS OF THE BRIGHTEST FLARE SEEN FROM Sgr A*

^{+0.3}_{-0.4}\times 10 ^{35}