Chandra X-ray observation of the young stellar cluster NGC 3293 in the Carina Nebula Complex

We characterize the stellar population of the poorly explored young stellar cluster NGC 3293 at the northwestern periphery of the Carina Nebula Complex, in order to evaluate the cluster age and the mass function, and to test claims of an abnormal IMF and a deficit of M <= 2.5 M_sun stars. We performed a deep (70 ksec) X-ray observation of NGC 3293 with Chandra and detected 1026 individual X-ray point sources. We identify counterparts for 74% of the X-ray sources in deep near-infrared images. Our data clearly show that NGC 3293 hosts a large population of solar-mass stars, refuting claims of a lack of M <= 2.5 M_sun stars. The analysis of the color magnitude diagram suggests an age of ~8-10 Myr for the low-mass population of the cluster. There are at least 511 X-ray detected stars with color magnitude positions that are consistent with young stellar members within 7 arcmin of the cluster center. The number ratio of X-ray detected stars in the 1-2 M_sun range versus the M >= 5 M_sun stars (known from optical spectroscopy) is consistent with the expectation from a normal field initial mass function. Most of the early B-type stars and 20% of the later B-type stars are detected as X-ray sources. Our data shows that NGC 3293 is one of the most populous stellar clusters in the entire Carina Nebula Complex. The cluster probably harbored several O-type stars, whose supernova explosions may have had an important impact on the early evolution of the Carina Nebula Complex.Comment: accepted for Astronomy & Astrophysic

Parsec-scale X-ray Flows in High-mass Star-forming Regions

The Chandra X-ray Observatory is providing remarkable new views of massive star-forming regions, revealing all stages in the life cycle of high-mass stars and their effects on their surroundings. We present a Chandra tour of several high-mass star-forming regions, highlighting physical processes that characterize the life of a cluster of high-mass stars, from deeply-embedded cores too young to have established an HII region to superbubbles so large that they shape our views of galaxies. Along the way we see that X-ray observations reveal hundreds of stellar sources powering great HII region complexes, suffused by both hard and soft diffuse X-ray structures caused by fast O-star winds thermalized in wind-wind collisions or by termination shocks against the surrounding media. Finally, we examine the effects of the deaths of high-mass stars that remained close to their birthplaces, exploding as supernovae within the superbubbles that these clusters created. We present new X-ray results on W51 IRS2E and 30 Doradus and we introduce new data on Trumpler 14 in Carina and the W3 HII region complexes W3 Main and W3(OH).Comment: 6 pages, 3 figures, to appear in the proceedings of IAU Symposium 227,"Massive Star Birth - A Crossroads of Astrophysics," eds. R. Cesaroni, E. Churchwell, M. Felli, and C.M. Walmsle

Mitigating Charge Transfer Inefficiency in the Chandra X-ray Observatory's ACIS Instrument

The ACIS front-illuminated CCDs onboard the Chandra X-ray Observatory were damaged in the extreme environment of the Earth's radiation belts, resulting in enhanced charge transfer inefficiency (CTI). This produces a row dependence in gain, event grade, and energy resolution. We model the CTI as a function of input photon energy, including the effects of de-trapping (charge trailing), shielding within an event (charge in the leading pixels of the 3X3 event island protect the rest of the island by filling traps), and non-uniform spatial distribution of traps. This technique cannot fully recover the degraded energy resolution, but it reduces the position dependence of gain and grade distributions. By correcting the grade distributions as well as the event amplitudes, we can improve the instrument's quantum efficiency. We outline our model for CTI correction and discuss how the corrector can improve astrophysical results derived from ACIS data.Comment: Accepted by ApJ Letters; see http://www.astro.psu.edu/users/townsley/cti

The cataclysmic variable SDSS J1507+52: An eclipsing period bouncer in the Galactic halo

SDSS J1507+52 is an eclipsing cataclysmic variable consisting of a cool, non-radially pulsating white dwarf and an unusually small sub-stellar secondary. The system has a high space velocity and a very short orbital period of about 67 minutes, well below the usual minimum period for CVs. To explain the existence of this peculiar system, two theories have been proposed. One suggests that SDSS J1507+52 was formed from a detached white-dwarf/brown-dwarf binary. The other theory proposes that the system is a member of the Galactic halo-population. Here, we present ultraviolet spectroscopy of SDSS J1507+52 obtained with the Hubble Space Telescope with the aim of distinguishing between these two theories. The UV flux of the system is dominated by emission from the accreting white dwarf. Fits to model stellar atmospheres yield physical parameter estimates of T(eff) = 14200 \pm 500 K, log(g)=8.2 \pm 0.3, vsin(i)=180 \pm 20 kms-1 and [Fe/H]=-1.2 \pm 0.2. These fits suggest a distance towards SDSS J1507+52 of d = 250 \pm 50 pc. The quoted uncertainties include systematic errors associated with the adopted fitting windows and interstellar reddening. Assuming that there is no contribution to the UV flux from a hot, optically thick boundary layer, we find a T(eff) much higher than previously estimated from eclipse analysis. The strongly sub-solar metallicity we infer for SDSS J1507+52 is consistent with that of halo stars at the same space velocity. We therefore conclude that SDSS J1507+52 is a member of the Galactic halo

Assessing reservoir operations risk under climate change

Risk-based planning offers a robust way to identify strategies that permit adaptive water resources management under climate change. This paper presents a flexible methodology for conducting climate change risk assessments involving reservoir operations. Decision makers can apply this methodology to their systems by selecting future periods and risk metrics relevant to their planning questions and by collectively evaluating system impacts relative to an ensemble of climate projection scenarios (weighted or not). This paper shows multiple applications of this methodology in a case study involving California\u27s Central Valley Project and State Water Project systems. Multiple applications were conducted to show how choices made in conducting the risk assessment, choices known as analytical design decisions, can affect assessed risk. Specifically, risk was reanalyzed for every choice combination of two design decisions: (1) whether to assume climate change will influence flood-control constraints on water supply operations (and how), and (2) whether to weight climate change scenarios (and how). Results show that assessed risk would motivate different planning pathways depending on decision-maker attitudes toward risk (e.g., risk neutral versus risk averse). Results also show that assessed risk at a given risk attitude is sensitive to the analytical design choices listed above, with the choice of whether to adjust flood-control rules under climate change having considerably more influence than the choice on whether to weight climate scenarios

Chandra Observations of SNR 1987A

We report on the results of our monitoring program of the X-ray remnant of supernova 1987A with the {\it Chandra X-Ray Observatory}. We have performed two new observations during the {\it Chandra} Cycle 3 period, bringing the total to six monitoring observations over the past three years. These six observations provide a detailed time history of the birth of a new supernova remnant in X-rays. The high angular resolution images indicate that soft X-ray bright knots are associated with the optical spots, while hard X-ray features are better correlated with radio images. We interpret this in terms of a model in which fast shocks propagating through the circumstellar HII region produce the hard X-ray and radio emission, while the soft X-ray and optical emission arise in slower shocks entering into dense knots in the circumstellar inner ring. New observations begin to show changes in the morphology that may herald a new stage in the development of this incipient supernova remnant. The observed X-ray fluxes increase by nearly a factor of three over the last 30 months. The X-ray remnant is expanding at a velocity of $\sim$5000 km s$^{-1}$.Comment: 8 pages, 6 figures, 2 color figures, To appear in AdSpR (Proceedings 34th COSPAR Synposium E1.4 "High Energy Studies of Supernova Remnants and Neutron stars" For high resolution color figures contact [email protected]

The Poultry Club I

Cooperative Extension Work in Agriculture and Home Economics, University of Missouri, College of Agriculture and the United States Department of Agriculture cooperating."March, 1923."Title from cover

The Diverse Stellar Populations of the W3 Star Forming Complex

An 800 sq-arcmin mosaic image of the W3 star forming complex obtained with the Chandra X-ray Observatory gives a valuable new view of the spatial structure of its young stellar populations. The Chandra image reveals about 1300 faint X-ray sources, most of which are PMS stars in the cloud. Some, but not all, of the high-mass stars producing hypercompact and ultracompact H II (UCHII) regions are also seen, as reported in a previous study. The Chandra images reveal three dramatically different embedded stellar populations. The W3 Main cluster extends over 7 pc with about 900 X-ray stars in a nearly-spherical distribution centered on the well-studied UCHII regions and high-mass protostars. The cluster surrounding the prototypical UCHII region W3(OH) shows a much smaller (<0.6 pc), asymmetrical, and clumpy distribution of about 50 PMS stars. The massive star ionizing the W3 North H II region is completely isolated without any accompanying PMS stars. In W3 Main, the inferred ages of the widely distributed PMS stars are significantly older than the inferred ages of the central OB stars illuminating the UCHIIs. We suggest that different formation mechanisms are necessary to explain the diversity of the W3 stellar populations: cluster-wide gravitational collapse with delayed OB star formation in W3 Main, collect-and-collapse triggering by shock fronts in W3(OH), and a runaway O star or isolated massive star formation in W3 North.Comment: To appear in the Astrophysical Journal. 21 pages, 5 figures. A version with high-quality figures is available at http://www.astro.psu.edu/users/edf/W3_Chandra.pd