Search Publications
The Hubble Space Telescope View of LINER Nuclei: Evidence for a Dual Population?
Chiaberge, Marco; Capetti, Alessandro; Macchetto, F. Duccio
We study a complete, distance-limited sample of 25 LINERs, 21 of which have been imaged with the Hubble Space Telescope. In nine objects we detect an unresolved nucleus. To study their physical properties, we compare the radio and optical properties of the nuclei of LINERs with those of other samples of local active galactic nuclei (AGNs), namely,…
Repeated X-Ray Flaring Activity in Sagittarius A*
Grosso, N.; Porquet, D.; Ferrando, P. +5 more
Investigating the spectral and temporal characteristics of the X-rays coming from Sagittarius A* (Sgr A*) is essential to our development of a more complete understanding of the emission mechanisms in this supermassive black hole located at the center of our Galaxy. Several X-ray flares with varying durations and spectral features have already bee…
Modeling Complete Distributions with Incomplete Observations: The Velocity Ellipsoid from Hipparcos Data
Hogg, David W.; Johnston, Kathryn V.; Blanton, Michael R. +1 more
An algorithm is developed to model the three-dimensional velocity distribution function of a sample of stars using only measurements of each star's two-dimensional tangential velocity. The algorithm works with ``missing data'': it reconstructs the three-dimensional distribution from data (velocity measurements) that all have one dimension that is …
Discovery of a 105 ms X-Ray Pulsar in Kesteven 79: On the Nature of Compact Central Objects in Supernova Remnants
Gotthelf, E. V.; Halpern, J. P.; Seward, F. D.
We report the discovery of 105 ms X-ray pulsations from the compact central object (CCO) in the supernova remnant Kes 79 using data acquired with the Newton X-Ray Multi-Mirror Mission (XMM-Newton). Two observations of the pulsar taken 6 days apart yield an upper limit on its spin-down rate of P˙<7×10-14 s s-1 and no eviden…
Revealing the Interaction between the X-Ray Gas of Starburst Galaxy UGC 6697 and the Hot Intracluster Medium of A1367
Vikhlinin, A.; Sun, M.
We present the result from a Chandra observation of an X-ray-luminous starburst galaxy, UGC 6697, which is embedded in the northwest hot region of A1367 (5-6 keV). A very sharp X-ray edge (~13-fold surface brightness jump) at the southeast and a long tail (at least 60 kpc from the nucleus) at the northwest of the galaxy are detected, as expected i…
The Acoustic Showerglass. I. Seismic Diagnostics of Photospheric Magnetic Fields
Braun, D. C.; Lindsey, Charles
A problem of major interest in the helioseismology of active regions is the acoustics of magnetic photospheres and shallow subphotospheres. Magnetic fields suppress the photospheric signatures of acoustic waves impinging onto them from the underlying solar interior and shift their phases. The phase shifts function as a sort of acoustic showerglass…
On the Origin of Exponential Disks at High Redshift
Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Vollbach, David R. +2 more
The major-axis and ellipse-fit intensity profiles of spiral galaxies larger than 0.3" in the Hubble Space Telescope Ultra Deep Field (UDF) are generally exponential, whereas the major-axis profiles in irregular disk galaxies, called clump clusters in our previous studies, are clearly not. Here we show that the deprojected positions of star-forming…
The Age and Progenitor Mass of Sirius B
Holberg, J. B.; Liebert, James; Williams, Kurtis A. +2 more
The Sirius AB binary system has masses that are well determined from many decades of astrometric measurements. Because of the well-measured radius and luminosity of Sirius A, we employed the TYCHO stellar evolution code to determine the age of the Sirius AB binary system accurately, at 225-250 Myr. Note that this fit requires the assumption of sol…
XMM-Newton Detection of Pulsations and a Spectral Feature in the X-Ray Emission of the Isolated Neutron Star 1RXS J214303.7+065419/RBS 1774
Treves, A.; Cropper, M.; Zane, S. +4 more
We report on the results of a deep XMM-Newton observation of RBS 1774, the most recent dim isolated neutron star candidate found in the ROSAT archive data. Spectral and timing analysis of the high-quality pn and MOS data confirm the association of this source with an isolated neutron star. The spectrum is thermal and blackbody-like, and there is e…
Mass Segregation and the Initial Mass Function of Super Star Cluster M82-F
Graham, James R.; McCrady, Nate; Vacca, William D.
We investigate the initial mass function and mass segregation in super star cluster M82-F with high-resolution Keck NIRSPEC echelle spectroscopy. Cross-correlation with template supergiant spectra provides the velocity dispersion of the cluster, enabling measurement of the kinematic (virial) mass of the cluster when combined with sizes from NICMOS…