XMM-Newton observation of the young open cluster Blanco 1. I. X-ray spectroscopy and photometry

We present an X-ray study of the high metallicity young open cluster Blanco 1 based on XMM--Newton data. X-ray spectroscopy of cluster members is presented for the first time as well as new X-ray distribution functions of late-type stars. We detected all known dF and dG stars in the EPIC field and 80% and 90% of dK and dM stars, respectively. The X-ray spectral analysis of the X-ray brightest cluster stars and X-ray color analysis of a larger sample show that a model with two temperatures (at about 0.3 and 1 keV) explains the quiescent activity phase spectra. We discuss also the nature of unidentified X-ray sources in the observed region and their X-ray spectral properties.Comment: 18 pages, 8 figures, paper accepted for publication on A&

Rotational modulation of X-ray emission in Orion Nebula young stars

We investigate the spatial distribution of X-ray emitting plasma in a sample of young Orion Nebula Cluster stars by modulation of their X-ray light-curves due to stellar rotation. The study, part of the Chandra Orion Ultradeep Project (COUP), is made possible by the exceptional length of the observation: 10 days of ACIS integration during a time span of 13 days, yielding a total of 1616 detected sources in the 17x17 arcmin field of view. We here focus on a subsample of 233 X-ray-bright stars with known rotational periods. We search for X-ray modulation using the Lomb Normalized Periodogram method. X-ray modulation related to the rotation period is detected in at least 23 stars with periods between 2 and 12 days and relative amplitudes ranging from 20% to 70%. In 16 cases, the X-ray modulation period is similar to the stellar rotation period while in seven cases it is about half that value, possibly due to the presence of X-ray emitting structures at opposite stellar longitudes. These results constitute the largest sample of low mass stars in which X-ray rotational modulation has been observed. The detection of rotational modulation indicates that the X-ray emitting regions are distributed inhomogeneneously in longitude and do not extend to distances significantly larger than the stellar radius. Modulation is observed in stars with saturated activity levels (L_X/L_bol ~ 10^(-3)) showing that saturation is not due to the filling of the stellar surface with X-ray emitting regions.Comment: 41 pages, 15 figures, ApJS in press. Figure 15 (34 panels) is an on-line only figure and is not included. A pdf file which includes figure 15 as well as full resolution versions of figure 10 and 11 is available at: http://www.astropa.unipa.it/~ettoref/COUP_RotMod.pd

High-amplitude, long-term X-ray variability in the solar-type star HD 81809: the beginning of an X-ray activity cycle?

We present the initial results from our XMM program aimed at searching for X-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhat more evolved than the Sun, and with a less massive companion) with a pronounced 8.2 yr chromospheric cycle, as evident from from the Mt. Wilson program data. We present here the results from the initial 2.5 years of XMM observations, showing that large amplitude (a factor of approx. 10) modulation is present in the X-ray luminosity, with a clearly defined maximum in mid 2002 and a steady decrease since then. The maximum of the chromospheric cycle took place in 2001; if the observed X-ray variability is the initial part of an X-ray cycle, this could imply a phase shift between chromospheric and coronal activity, although the current descent into chromospheric cycle minimum is well reflected into the star's X-ray luminosity. The observations presented here provide clear evidence for the presence of large amplitude X-ray variability coherent with the activity cycle in the chromosphere in a star other than the Sun.Comment: Accepted for publication in A&

A Deep Chandra X-Ray Observation of the Rich Young Cluster NGC 6530. I. The X-Ray Source Catalog and the Cluster Population

In ad eep 60 ksChandra ACIS X-ray observation of the very young cluster NGC 6530, we detect 884 X-ray point sources and argue that a very large fraction of them (90%-95%) must be pre-main-sequence (PMS) cluster members, mostly of low masses. This is a significant enlargement of the known NGC 6530 stellar population with respect to previous optical studies, including Hsurveys. We identify 220 X-ray sources with cataloged stars down to V ¼ 17, while most unidentified sources have fainter counterparts. Moreover, we find an infrared counterpart in the 2MASS catalog for 731 X-ray sources. The optically identified cluster X-ray sources are found in a band in the H-R diagram above the main sequence, in the locus of 0.5-1.5 Myr PMS stars, with masses down to 0.5-1.5 M� . We find evidence of an age gradient across the field from northwest to south, suggesting a sequence of star formation events qualitatively similar to that found in earlier studies of the same region, but differing in the details. A group of X-ray sources showing frequent flares may be associated with the youngest stars in the cluster, suggesting that X-ray flaring activity is especially intense in the youngest PMS phases of low- mass stars. Subject headings: open clusters and associations: individual (NGC 6530) — stars: coronae — stars: pre-main-sequence — X-rays: star

A Mandated Minimum Competency Testing Program and Its Impact on Learning Disabled Students: Curricular Validity and Comparative Performances

This research was published by the KU Center for Research on Learning, formerly known as the University of Kansas Institute for Research in Learning Disabilities.In this study, LD specialists, regular class teachers, and parents of LD students judged that the objectives of the Kansas Minimum Competency Specifications prescribed for nonhandicapped students were applicable to LD students. In addition, the Kansas Minimal Competency Test was administered to LD students under standard and oral conditions. Results showed that they did not perform as well as their nonhandicapped peers at any of the five grade levels. The test was then administered under two modified conditions. Learning disabled students' performance on some objectives at every grade level was not improved by either administering items orally or administering the test one grade level above that designated for nonhandicapped students

Coronal Variability in the Young Cluster NGC 2516

NGC 2516 has been observed by Chandra several times in order to correct the plate scale of the spacecraft's focal plane instruments. Because of this, Chandra has observed NGC 2516 with all four imaging arrangements available. In addition, NGC 2516 has been observed as part of the High Resolution Camera (HRC) guaranteed time program and is scheduled for return plate scale calibration visits. This makes it the best cluster to study for long-term variability. NGC 2516 is about 140 Myr old and less than 400 pc away. In our first paper, we discussed the detection of 150 X-ray sources (42% of which are identified as cluster members) in the calibration data taken during the orbital activation phase of the Chandra mission. In our second paper, we combined all the extant data sets and detected 284 sources, more than half of which are considered likely cluster members. In this our third paper, we further explore techniques of combining Advanced CCD Imaging Spectrometer (ACIS) and HRC Chandra data for timing analysis. We have been able to combine almost 70 ks of observation time, spread over five epochs, to study variability in this cluster on multiple timescales. We find that while stochastic variability rates are about the same for all objects in the sample, the timescale for detecting variability is shorter for late-type stars. Both stochastic and flare variability rates seen in NGC 2516 are similar to those seen in younger clusters IC 348, NGC 1333, and M42

Stellar Activity on the Young Suns of Orion: COUP Observations of K5-7 Pre-Main Sequence Stars

In January 2003, the Chandra Orion Ultradeep Project (COUP) detected about 1400 young stars during a 13.2 day observation of the Orion Nebula Cluster (ONC). This paper studies a well-defined sample of 28 solar-mass COUP sources to characterize the magnetic activity of analogs of the young Sun and thereby to improve understanding of the effects of solar X-rays on the solar nebula during the era of planet formation. We find that active young Suns spend 70% of their time in a characteristic state with relatively constant flux and magnetically confined plasma with temperatures kT_2 = 2.1 * kT_1. During characteristic periods, the 0.5-8 keV X-ray luminosity is about 0.03% of the bolometric luminosity. One or two powerful flares per week with peak luminosities logL_x ~ 30-32 erg/s are typically superposed on this characteristic emission accompanied by heating of the hot plasma component from ~2.4 keV to ~7 keV at the flare peak. The energy distribution of flares superposed on the characteristic emission level follows the relationship dN/dE ~ E^-1.7. The flare rates are consistent with the production of sufficiently energetic protons to spawn a spallogenic origin of some important short-lived radionuclides found in ancient meteorites. The X-rays can ionize gas in the circumstellar disk at a rate of 6 10^-9 ionizations per second at 1 AU from the central star, orders of magnitude above cosmic ray ionization rates. The estimated energetic particle fluences are sufficient to a account for many isotopic anomalies observed in meteoritic inclusions.Comment: 49 pages, 12 figures. Accepted for publication in the Astrophysical Journal Supplements, COUP Special Issue (Oct 2005). For version with higher quality figures, see http://www.astro.psu.edu/coup/Suns.htm

Chandra X-Ray Observatory -First Year Science Highlights

Abstract. The Chandra X-ray Observatory achieved orbit on July 23, 1999, and began science observing in October 1999. Now over a year since the first light image of Cas-A, Chandra has observed several hundred science targets and many calibration objects. A few highlights from these data are presented -including a discussion of the spatially resolved spectrum of supernova ejecta in Cas-A and X-ray emission from the central regions of M31, the nearby AGN Cen-A, and the quasar 3C273