Amy E. Mossman

Ubvri light curves of 44 type ia supernovae

We present UBVRI photometry of 44 Type Ia supernovae (SNe 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 SNe Ia to date, nearly doubling the number of well-observed, nearby SNe Ia with published multicolor CCD light curves. The large sample of U-band photometry is a unique addition, with important connections to SNe 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 the B band.

A FULL YEAR'S CHANDRA EXPOSURE ON SLOAN DIGITAL SKY SURVEY QUASARS FROM THE CHANDRA MULTIWAVELENGTH PROJECT

We study the spectral energy distributions and evolution of a large sample of optically selected quasars from the Sloan Digital Sky Survey that were observed in 323 Chandra images analyzed by the Chandra Multiwavelength Project. Our highest-confidence matched sample includes 1135 X-ray detected quasars in the redshift range 0.2 3, substantially expanding the known sample. We find no evidence for evolution out to z ~ 5 for either the X-ray photon index Γ or for the ratio of optical/UV to X-ray flux αox. About 10% of detected QSOs show best-fit intrinsic absorbing columns greater than 1022 cm–2, but the fraction might reach ~1/3 if most nondetections are absorbed. We confirm a significant correlation between αox and optical luminosity, but it flattens or disappears for fainter (MB –23) active galactic nucleus (AGN) alone. We report significant hardening of Γ both toward higher X-ray luminosity, and for relatively X-ray loud quasars. These trends may represent a relative increase in nonthermal X-ray emission, and our findings thereby strengthen analogies between Galactic black hole binaries and AGN. For uniformly selected subsamples of narrow-line Seyfert 1s and narrow absorption line QSOs, we find no evidence for unusual distributions of either αox or Γ.

ChaMP Serendipitous Galaxy Cluster Survey

We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13 deg 2 , we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about � 10 � 14 ergs cm � 2 s � 1 , with a median cluster core radius of 21 00 . For 56 of the 130 X-ray fields, we use the ChaMP’s deep NOAO 4 m MOSAIC g 0 , r 0 , and i 0 imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore- and background contamination and provides photometric redshifts to z � 0:7. From the overlapping 6.1 deg 2 X-ray/optical imaging, wefind115opticalclusters (ofwhich11%areintheX-raycatalog)and28X-rayclusters(ofwhich46%are in the optical VTP catalog). The median redshift of the 13 X-ray/optical clusters is 0.41, and their median X-ray luminosity (0.5‐2 keV) is LX ¼ 2:65 � 0:19 ðÞ ; 10 43 ergs s � 1 . The clusters in our sample that are only detected in our optical data are poorer on average (� 4 � ) than the X-ray/optically matched clusters, which may partially explain the difference in the detection fractions. Subject headingg galaxies: clusters: general — surveys — X-rays: galaxies: clusters

The Chandra Multi-wavelength Project: Optical Spectroscopy and the Broadband Spectral Energy Distributions of X-Ray-selected AGNs.

From optical spectroscopy of X-ray sources observed as part of the Chandra Multi-wavelength Project (ChaMP), we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow-up using the FLWO/1.5 m, SAAO/1.9 m, WIYN 3.5 m, CTIO/4 m, KPNO/4 m, Magellan/6.5 m, MMT/6.5 m, and Gemini/8 m telescopes, and from archival Sloan Digital Sky Survey (SDSS) spectroscopy. We classify the optical counterparts as 50% broad-line active galactic nuclei (AGNs), 16% emission line galaxies, 14% absorption line galaxies, and 20% stars. We detect QSOs out to z ~ 5.5 and galaxies out to z ~ 3. We have compiled extensive photometry, including X-ray (ChaMP), ultraviolet (GALEX), optical (SDSS and ChaMP-NOAO/MOSAIC follow-up), near-infrared (UKIDSS, Two Micron All Sky Survey, and ChaMP-CTIO/ISPI follow-up), mid-infrared (WISE), and radio (FIRST and NVSS) bands. Together with our spectroscopic information, this enables us to derive detailed spectral energy distributions (SEDs) for our extragalactic sources. We fit a variety of template SEDs to determine bolometric luminosities, and to constrain AGNs and starburst components where both are present. While ~58% of X-ray Seyferts (1042 erg s–1 5% starburst contribution to bolometric luminosity) to fit observed photometry only 26% of the X-ray QSO (L 2 – 10 keV >1044 erg s–1) population appear to have some kind of star formation contribution. This is significantly lower than for the Seyferts, especially if we take into account torus contamination at z > 1 where the majority of our X-ray QSOs lie. In addition, we observe a rapid drop of the percentage of starburst contribution as X-ray luminosity increases. This is consistent with the quenching of star formation by powerful QSOs, as predicted by the merger model, or with a time lag between the peak of star formation and QSO activity. We have tested the hypothesis that there should be a strong connection between X-ray obscuration and star formation but we do not find any association between X-ray column density and star formation rate both in the general population or the star-forming X-ray Seyferts. Our large compilation also allows us to report here the identification of 81 X-ray Bright Optically inactive Galaxies, 78 z > 3 X-ray sources, and eight Type-2 QSO candidates. Also, we have identified the highest redshift (z = 5.4135) X-ray-selected QSO with optical spectroscopy.

Chandra multiwavelength project: normal galaxies at intermediate redshift

We investigate Chandra extragalactic sources, including galaxies with narrow emission line (NELG) and absorption line galaxies (ALG), but excluding broad emission line AGNs and quasars. Based on f_{X}/f_{O}, L_{X}, X-ray spectral hardness and optical emission line diagnostics, we have conservatively classified normal galaxies. With our ChaMP galaxy sample (extended to include 6 years of Chandra data) and additional normal galaxies found in other X-ray surveys, we discuss their L_{X}/L_{B} evolution, log(N)-log(S) relationship, off-nucleus ULXs, XBONGs, and E+A galaxies.

Variable stars in the Pegasus dwarf galaxy (DDO 216)

Observations obtained over a period of five years of the resolved stars in the Pegasus dwarf irregular galaxy (DDO 216) have been searched for variable stars. Thirty-one variables were found, and periods established for 12. Two of these variable stars are clearly eclipsing variables, seven are very likely Cepheid variables, and the remaining three are probable Cepheids. The period-luminosity relation for the Cepheids indicates a distance modulus for Pegasus of m - M = 26.22 + or - 0.20. This places Pegasus very near the zero-velocity surface of the Local Group. 25 refs.

The ChaMP Extended Stellar Survey (ChESS): Photometric and Spectroscopic Properties of Serendipitously Detected Stellar X-Ray Sources

We present 348 X-ray-emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a wide-area serendipitous survey based on archival X-ray images, with the Sloan Digital Sky Survey (SDSS). We use morphological star/galaxy separation, matching to an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data-quality tests to create our catalog, the ChaMP Extended Stellar Survey (ChESS), from a sample of 2121 matched ChaMP/SDSS sources. Our cuts retain 92% of the spectroscopically confirmed stars in the original sample while excluding 99.6% of the 684 spectroscopically confirmed extragalactic sources. Fewer than 3% of the sources in our final catalog are previously identified stellar X-ray emitters. For 42 catalog members, spectroscopic classifications are available in the literature. We present new spectral classifications and Hα measurements for an additional 79 stars. The catalog is dominated by main-sequence stars; we estimate the fraction of giants in ChESS is ~10%. We identify seven giant stars (including a possible Cepheid and an RR Lyrae star) as ChaMP sources, as well as three cataclysmic variables. We derive distances from ~10 to 2000 pc for the stars in our catalog using photometric parallax relations appropriate for dwarfs on the main sequence and calculate their X-ray and bolometric luminosities. These stars lie in a unique space in the LX-distance plane, filling the gap between the nearby stars identified as counterparts to sources in the ROSAT All Sky Survey and the more distant stars detected in deep Chandra and XMM-Newton surveys. For 36 newly identified X-ray-emitting M stars we calculate LHα/Lbol. The quantities LHα/Lbol and LX/Lbol are linearly related below -->LX/Lbol ~ 3 × 10−4, while LHα/Lbol appears to turn over at larger LX/Lbol values. Stars with reliable SDSS photometry have an ~0.1 mag blue excess in -->u − g, likely due to increased chromospheric continuum emission. Photometric metallicity estimates suggest that the sample is evenly split between the young and old disk populations of the Galaxy; the lowest activity sources belong to the old disk population, a clear signature of the decay of magnetic activity with age. Future papers will present analyses of source variability and comparisons of this catalog to models of stellar activity in the Galactic disk.

STATISTICAL CHARACTERIZATION OF THE CHANDRA SOURCE CATALOG

The first release of the Chandra Source Catalog (CSC) contains ~95,000 X-ray sources in a total area of 0.75% of the entire sky, using data from ~3900 separate ACIS observations of a multitude of different types of X-ray sources. In order to maximize the scientific benefit of such a large, heterogeneous data set, careful characterization of the statistical properties of the catalog, i.e., completeness, sensitivity, false source rate, and accuracy of source properties, is required. Characterization efforts of other large Chandra catalogs, such as the ChaMP Point Source Catalog or the 2 Mega-second Deep Field Surveys, while informative, cannot serve this purpose, since the CSC analysis procedures are significantly different and the range of allowable data is much less restrictive. We describe here the characterization process for the CSC. This process includes both a comparison of real CSC results with those of other, deeper Chandra catalogs of the same targets and extensive simulations of blank-sky and point-source populations.

Radio, visible, and X ray emission preceding and following a coronal mass ejection

This study uses both disk and limb observations to examine the changing conditions of the low solar corona, below 1.5 R s , preceding and following a coronal mass ejection observed on the west limb on April 12, 1993. The disk observations comprise 90 cm (333 MHz) radio and daily Yohkoh soft X ray measurements, while the limb observations include measurements of emission from X rays, Fe X 637.4 nm and Fe XIV 530.3 nm coronal lines, and broadband Thomson-scattered white light. The analysis of the disk and limb observations shows that throughout the 3 days of consecutive observations, the occurrence and persistence of nonthermal emission at 90 cm, also known as type I noise storm emission, were associated with large-scale magnetic structures where the coronal mass ejection eventually occurred. Other than a subsequent flare observed in X rays at the limb, the changes in the coronal emission preceding and following the event were not markedly different from changes in other neighboring structures. The analysis of this novel combination of data supports the current view that coronal mass ejections are a cause rather than a consequence of the classical solar activity in the low corona. The radio observations, on the other hand, suggest that a connection between a noise storm and a coronal mass ejection exists. However, they do not necessarily imply that the noise storm actually initiates the event.

Demonstrating the limitations of line ratio temperature diagnostic using Fe X and Fe XIV spectral line intensity observations

The electron temperature in the inner corona can be derived from spectral line intensity measurements by comparing the ratio of the measured intensities of two spectral lines to the ratio calculated from theoretical models. In a homogeneous plasma the line ratio technique can be used for any two lines if the ratio of the intensities is independent of the density. The corona, however, is far from homogeneous and usually several distinct structures are present along the line-of-sight. For example, even the large polar coronal holes at solar minimum can be partly or completely obscured by emission from hotter and denser surrounding regions. In this case the structures that contribute to the line intensity do not occupy the same volume if the peak temperature of the spectral lines are too widely separated. We demonstrate this effect for the southern polar coronal hole, using daily intensity measurements of the Fe XIV 5303 A and Fe X 6374 A spectral lines from the National Solar Observatory at Sacramento Peak ...