[Show abstract][Hide abstract] ABSTRACT: We map the full extent of a rich massive young cluster in the Cep OB3b association with the Infrared Array Camera and Multi-band Imaging Photometer System instruments aboard the Spitzer Space Telescope and the ACIS instrument aboard the Chandra X-Ray Observatory. At 700 pc, it is revealed to be the second nearest large (>1000 member), young (<5 Myr) cluster known. In contrast to the nearest large cluster, the Orion Nebula Cluster, Cep OB3b is only lightly obscured and is mostly located in a large cavity carved out of the surrounding molecular cloud. Our infrared and X-ray data sets, as well as visible photometry from the literature, are used to take a census of the young stars in Cep OB3b. We find that the young stars within the cluster are concentrated in two sub-clusters; an eastern sub-cluster, near the Cep B molecular clump, and a western sub-cluster, near the Cep F molecular clump. Using our census of young stars, we examine the fraction of young stars with infrared excesses indicative of circumstellar disks. We create a map of the disk fraction throughout the cluster and find that it is spatially variable. Due to these spatial variations, the two sub-clusters exhibit substantially different average disk fractions from each other: 32% ± 4% and 50% ± 6%. We discuss whether the discrepant disk fractions are due to the photodestruction of disks by the high mass members of the cluster or whether they result from differences in the ages of the sub-clusters. We conclude that the discrepant disk fractions are most likely due to differences in the ages.
The Astrophysical Journal 05/2012; 750:125. · 6.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe Chandra/ACIS-I observations of the massive ~ 13-14 Myr-old cluster, h Persei, part of the famous Double Cluster (h and χ Persei) in Perseus. Combining the list of Chandra-detected sources with new optical/IR photometry and optical spectroscopy reveals ~ 165 X-ray bright stars with V 23. Roughly 142 have optical magnitudes and colors consistent with cluster membership. The observed distribution of Lx peaks at Lx ~ 1030.3 erg s–1 and likely traces the bright edge of a far larger population of 0.4-2 M ☉ X-ray active stars. From a short list of X-ray active stars with IRAC 8 μm excess from warm, terrestrial zone dust, we derive a maximum X-ray flux incident on forming terrestrial planets. Although there is no correlation between X-ray activity and IRAC excess, the fractional X-ray luminosity correlates with optical colors and spectral type. By comparing the distribution of Lx /L versus spectral type and V – I in h Per with results for other 1-100 Myr-old clusters, we show that stars slightly more massive than the Sun ( 1.5 M ☉) fall out of X-ray saturation by 10-15 Myr. Changes in stellar structure for 1.5 M ☉ stars likely play an important role in this decline of X-ray emission.
The Astronomical Journal 01/2009; 137(2):3210. · 4.97 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Chandra X-ray Observatory was launched in July, 1999 and has yielded
extraordinary scientific results. Behind the scenes, our Monitoring and
Trends Analysis (MTA) system has proven to be a valuable resource. With
three years worth of on-orbit data, we have available a vast array of
both telescope diagnostic information and analysis of scientific data to
access Observatory performance. As part of Chandra's Science Operations
Team (SOT), the primary goal of MTA is to provide tools for effective
decision making leading to the most efficient production of quality
science output from the Observatory. We occupy a middle ground between
flight operations, chiefly concerned with the health and safety of the
spacecraft, and validation and verification, concerned with the
scientific validity of the data taken and whether or not they fulfill
the observer's requirements. In that role we provide and receive support
from systems engineers, instrument experts, operations managers, and
scientific users. MTA tools, products, and services include real-time
monitoring and alert generation for the most mission critical
components, long term trending of all spacecraft systems, detailed
analysis of various subsystems for life expectancy or anomaly
resolution, and creating and maintaining a large SQL database of
relevant information. This is accomplished through the use of a wide
variety of input data sources and flexible, accessible programming and
analysis techniques. This paper will discuss the overall design of the
system, its evolution and the resources available.
Proceedings of SPIE - The International Society for Optical Engineering 12/2002; · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Chandra's Monitoring and Trends Analysis (M&TA) team utilizes a
series of database tables to store binned information about spacecraft
configuration and condition over the life of the mission. The
DATASEEKER was developed as an efficient means to specify a particular
set of this data and have it conveniently downloaded in a usable format.
In Chandra's brief operational life of a little over two years in orbit,
there are already well over 10 GB of data stored in approximately 50
relational database tables for the Science Operation Team to sift
through. DATASEEKER has made it possible to discriminately pull out
small subsets of these data in a matter of minutes.