Konstantin V. Getman

The Origin of T Tauri X-Ray Emission: New Insights from the Chandra Orion Ultradeep Project

The Chandra Orion Ultradeep Project (COUP) provides the most comprehensive data set ever acquired on the X-rayemissionofpre–main-sequencestars.Inthispaper,westudythenearly600X-raysourcesthatcanbereliably identified with optically well-characterized T Tauri stars (TTSs) in the Orion Nebula Cluster. With a detection limit of LX; min � 10 27:3 ergs s � 1 for lightly absorbed sources, we detect X-ray emission from more than 97% of the optically visible late-type (spectral types F–M) cluster stars. This proves that there is no ‘‘X-ray–quiet’’ population of late-type stars with suppressed magnetic activity. We use this exceptional optical, infrared, and X-ray data set tostudythe dependenciesoftheX-rayproperties onotherstellarparameters. AllTTSs withknownrotationperiods lie in the saturated or supersaturated regime of the relation between activity and Rossby numbers seen for mainsequence (MS) stars, but the TTSs show a much larger scatter in X-ray activity than that seen for the MS stars. Strong near-linear relations between X-ray luminosities, bolometric luminosities, and mass are present. We also

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.

INNOVATIONS IN THE ANALYSIS OF CHANDRA-ACIS OBSERVATIONS

As members of the instrument team for the Advanced CCD Imaging Spectrometer (ACIS) on NASAs Chandra X-ray Observatory and as Chandra General Observers, we have developed a wide variety of data analysis methods that we believe are useful to the Chandra community, and have constructed a significant body of publicly available software (the ACIS Extract package) addressing important ACIS data and science analysis tasks. This paper seeks to describe these data analysis methods for two purposes: to document the data analysis work performed in our own science projects and to help other ACIS observers judge whether these methods may be useful in their own projects (regardless of what tools and procedures they choose to implement those methods). The ACIS data analysis recommendations we offer here address much of the workflow in a typical ACIS project, including data preparation, point source detection via both wavelet decomposition and image reconstruction, masking point sources, identification of diffuse structures, event extraction for both point and diffuse sources, merging extractions from multiple observations, nonparametric broadband photometry, analysis of low-count spectra, and automation of these tasks. Many of the innovations presented here arise from several, often interwoven, complications that are found in many Chandra projects: large numbers of point sources (hundreds to several thousand), faint point sources, misaligned multiple observations of an astronomical field, point source crowding, and scientifically relevant diffuse emission.

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.

Chandra Study of Young Stellar Objects in the NGC 1333 Star-forming Cloud

NGC 1333, a highly active star formation region within the Perseus molecular cloud complex, has been observed with the ACIS-I detector on board the Chandra X-Ray Observatory. In our image with a sensitivity limit of ~1028 ergs s-1, we detect 127 X-ray sources, most with subarcsecond positional accuracy. While 32 of these sources appear to be foreground stars and extragalactic background, 95 X-ray sources are identified with known cluster members. The X-ray luminosity function of the discovered young stellar object (YSO) population spans a range of log LX 28.0-31.5 ergs s-1 in the 0.5-8 keV band, and absorption ranges from log NH 20 to 23 cm-2. Most of the sources have plasma energies between 0.6 and 3 keV, but a few sources show higher energies up to ~7 keV. Comparison with K-band source counts indicates that we detect all of the known cluster members with K 12. K 11, the peak of the K-band luminosity function, corresponds to 0.2-0.4 M☉ stars for a cluster age of ~1 Myr. We detect seven of the 20 known YSOs in NGC 1333 producing jets or molecular outflows as well as one deeply embedded object without outflows. No evident difference in X-ray emission of young stars with and without outflows is found. Based on the complete subsample of T Tauri stars, we also find no difference in X-ray properties and X-ray production mechanism of stars with and without K-band excess disks. Several other results are obtained. We suggest that the X-ray emission from two late B stars that illuminate the reflection nebula originates from unresolved late-type companions. Two T Tauri stars are discovered in the ACIS images as previously unknown components of visual binaries. A good correlation LX J is seen, which confirms the well-known relation LX Lbol found in many star-forming regions. Based on spectral analysis for the X-ray counterpart of SVS 16, we establish that the column density NH is much lower than that expected from near-IR photometry so that its X-ray luminosity, log LX 30.6 ergs s-1, is not unusually high.

The Young Stellar Population in M17 Revealed by Chandra

We report here results from a Chandra ACIS observation of the stellar populations in and around the M17 H II region. The field reveals 886 sources with observed X-ray luminosities (uncorrected for absorption) between similar to 29.3 ergs s(-1) < log L(X) < 32.8 ergs s(-1), 771 of which have stellar counterparts in infrared images. In addition to comprehensive tables of X-ray source properties, several results are presented:

AN INTRODUCTION TO THE CHANDRA CARINA COMPLEX PROJECT

The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatorys Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carinas regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of > 14,000 X-ray point sources;> 9800 of them have multiwavelength counterparts. Using Chandras unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carinas massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results.

X-Ray Study of Triggered Star Formation and Protostars in IC 1396N

The IC 1396N cometary globule (CG) within the large nearby H II region IC 1396 has been observed with the ACIS detector on board the Chandra X-Ray Observatory. We detect 117 X-ray sources, of which ~50-60 are likely members of the young open cluster Trumpler 37 dispersed throughout the H II region, and 25 are associated with young stars formed within the globule. Infrared photometry (2MASS and Spitzer) shows that the X-ray population is very young: 3 older Class III stars, 16 classical T Tauri stars, and 6 protostars including a Class 0/I system. We infer a total T Tauri population of ~30 stars in the globule, including the undetected population, with a star formation efficiency of 1%-4%. An elongated source spatial distribution with an age gradient oriented toward the exciting star is discovered in the X-ray population of IC 1396N, supporting similar findings in other cometary globules. The geometric and age distribution is consistent with the radiation-driven implosion (RDI) model for triggered star formation in CGs by H II region shocks. The inferred velocity of the shock front propagating into the globule is ~0.6 km s-1. The large number of X-ray-luminous protostars in the globule suggests either an unusually high ratio of Class I/0 to Class II/III stars or a nonstandard initial mass function favoring higher mass stars by the triggering process. We find that the Chandra source associated with the luminous Class 0/I protostar IRAS 21391+5802 is one of the youngest stars ever detected in the X-ray band. We also establish for the first time that the X-ray absorption in protostars arises from the local infalling envelopes rather than from ambient molecular cloud material.

A PAN-CARINA YOUNG STELLAR OBJECT CATALOG: INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE CARINA NEBULA IDENTIFIED VIA MID-INFRARED EXCESS EMISSION

We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42 deg2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope (the Vela-Carina survey) and the Two-Micron All Sky Survey. We model the 1-24 μm IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 M ☉ 2 × 104 YSOs and a present-day star formation rate (SFR) of >0.008 M ☉ yr–1. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.

A Chandra Study of the Rosette Star-forming Complex. I. The Stellar Population and Structure of the Young Open Cluster NGC 2244

We present the first high spatial resolution X-ray study of NGC 2244, the 2 Myr old stellar cluster in the Rosette Nebula, using Chandra. Over 900 X-ray sources are detected; 77% have optical or FLAMINGOS NIR stellar counterparts and are mostly previously uncataloged young cluster members. The X-ray-selected population is estimated to be nearly complete between 0.5 and 3 M☉. A number of further results emerge from our analysis: (1) The X-ray LF and the associated K-band LF indicate a normal Salpeter IMF for NGC 2244. This is inconsistent with the top-heavy IMF reported from earlier optical studies that lacked a good census of log (LX/Lbol) ~ − 7 relation. The Rosette OB X-ray spectra are soft and consistent with the standard model of small-scale shocks in the inner wind of a single massive star.