279 research outputs found
Carina OB Stars: X-ray Signatures of Wind Shocks and Magnetic Fields
The Chandra Carina Complex contains 200 known O- and B type stars. The
Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars.
We have assembled a publicly available optical/X-ray database to identify OB
stars that depart from the canonical Lx/Lbol relation, or whose average X-ray
temperatures exceed 1 keV. Among the single O stars with high kT we identify
two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS
1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable
X-rays, suggesting it may be a massive binary with a period of >30 days. The
visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission
components, suggesting embedded wind shocks close to the O2 If* Aa primary, and
colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic
binaries, the long orbital-period systems HD 93343, HD 93403 and QZ Car have
higher shock temperatures than short-period systems such as HD 93205 and FO 15.
Although the X-rays from most B stars may be produced in the coronae of unseen,
low-mass pre-main-sequence companions, a dozen B stars with high Lx cannot be
explained by a distribution of unseen companions. One of these, SS73 24 in the
Treasure Chest cluster, is a new candidate Herbig Be star.Comment: To be published in a special issue of the Astrophysical Journal
Supplement on the Chandra Carina Complex Projec
Managing Radiation Degradation of CCDs on the Chandra X-Ray Observatory--III
The CCDs on the Chandra X-ray Observatory are vulnerable to radiation damage from low-energy protons scattered off the telescope's mirrors onto the focal plane. Following unexpected damage incurred early in the mission, the Chandra team developed, implemented, and maintains a radiation-protection program. This program--involving scheduled radiation safing during radiation-belt passes, intervention based upon real-time space-weather conditions and radiation-environment modeling, and on-board radiation monitoring with autonomous radiation safing--has successfully managed the radiation damage to the CCDs. Since implementing the program, the charge-transfer inefficiency (CTI) has increased at an average annual rate of only 3.2x 10(exp -6) (2.3 percent) for the front-illuminated CCDs and 1.0x10(exp -6) (6.7 percent) for the back-illuminated CCDs. This paper describes the current status of the Chandra radiation-management program, emphasizing enhancements implemented since the previous papers
Prevention and early detection of prostate cancer
This Review was sponsored and funded by the International Society of Cancer Prevention (ISCaP), the European Association of Urology (EAU), the National Cancer Institute, USA (NCI) (grant number 1R13CA171707-01), Prostate Cancer UK, Cancer Research UK (CRUK) (grant number C569/A16477), and the Association for International Cancer Research (AICR
UBVRI Light Curves of 44 Type Ia Supernovae
We present UBVRI photometry of 44 type-Ia supernovae (SN Ia) observed from
1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence
Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The
data set comprises 2190 observations and is the largest homogeneously observed
and reduced sample of SN Ia to date, nearly doubling the number of
well-observed, nearby SN Ia with published multicolor CCD light curves. The
large sample of U-band photometry is a unique addition, with important
connections to SN Ia observed at high redshift. The decline rate of SN Ia
U-band light curves correlates well with the decline rate in other bands, as
does the U-B color at maximum light. However, the U-band peak magnitudes show
an increased dispersion relative to other bands even after accounting for
extinction and decline rate, amounting to an additional ~40% intrinsic scatter
compared to B-band.Comment: 84 authors, 71 pages, 51 tables, 10 figures. Accepted for publication
in the Astronomical Journal. Version with high-res figures and electronic
data at http://astron.berkeley.edu/~saurabh/cfa2snIa
Galaxies in X-ray Groups I: Robust Membership Assignment and the Impact of Group Environments on Quenching
Understanding the mechanisms that lead dense environments to host galaxies
with redder colors, more spheroidal morphologies, and lower star formation
rates than field populations remains an important problem. As most candidate
processes ultimately depend on host halo mass, accurate characterizations of
the local environment, ideally tied to halo mass estimates and spanning a range
in halo mass and redshift are needed. In this work, we present and test a
rigorous, probabalistic method for assigning galaxies to groups based on
precise photometric redshifts and X-ray selected groups drawn from the COSMOS
field. The groups have masses in the range 10^13 < M_200c/M_sun < 10^14 and
span redshifts 0<z<1. We characterize our selection algorithm via tests on
spectroscopic subsamples, including new data obtained at the VLT, and by
applying our method to detailed mock catalogs. We find that our group member
galaxy sample has a purity of 84% and completeness of 92% within 0.5 R200c. We
measure the impact of uncertainties in redshifts and group centering on the
quality of the member selection with simulations based on current data as well
as future imaging and spectroscopic surveys. As a first application of our new
group member catalog which will be made publicly available, we show that member
galaxies exhibit a higher quenched fraction compared to the field at fixed
stellar mass out to z~1, indicating a significant relationship between star
formation and environment at group scales. We also address the suggestion that
dusty star forming galaxies in such groups may impact the high-l power spectrum
of the cosmic microwave background and find that such a population cannot
explain the low power seen in recent SZ measurements.Comment: ApJ accepted. Catalogs will be posted at IRSA upon publication,
currently available upon reques
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 HII 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 60ks pointings using the
Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for
understanding recent and ongoing star formation and to probe Carina's 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 Chandra's 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 Carina's 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.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
least. 43 pages; 18 figure
Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304 in May 1994. I. The Ground-Based Campaign
Optical, near-infrared, and radio observations of the BL Lac object
PKS2155-304 were obtained simultaneously with a continuous UV/EUV/X-ray
monitoring campaign in 1994 May. Further optical observations were gathered
throughout most of 1994. The radio, millimeter, and near-infrared data show no
strong correlations with the higher energies. The optical light curves exhibit
flickering of 0.2-0.3 mag on timescales of 1-2 days, superimposed on longer
timescale variations. Rapid variations of ~0.01 mag/min, which, if real, are
the fastest seen to date for any BL Lac object. Small (0.2-0.3 mag) increases
in the V and R bands occur simultaneously with a flare seen at higher energies.
All optical wavebands (UBVRI) track each other well over the period of
observation with no detectable delay. For most of the period the average colors
remain relatively constant, although there is a tendency for the colors (in
particular B-V) to vary more when the source fades. In polarized light, PKS
2155-304 showed strong color dependence and the highest optical polarization (U
= 14.3%) ever observed for this source. The polarization variations trace the
flares seen in the ultraviolet flux.Comment: 45 pages, latex file with encapsulated postscript, accepted to the
Astrophysical Journa
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