Search Publications
A Method for Measuring Variations in the Stellar Initial Mass Function
Calzetti, D.; Kennicutt, R. C.; Lee, J. C. +3 more
We present a method for investigating variations in the upper end of the stellar initial mass function (IMF) by probing the production rate of ionizing photons in unresolved, compact star clusters with ages <=107 yr and with different masses. We test this method by performing a pilot study on the young cluster population in the nearb…
The Nature of the Hyper-Runaway Candidate Hip 60350
Przybilla, Norbert; Irrgang, Andreas; Heber, Ulrich +2 more
Young, massive stars in the Galactic halo are widely supposed to be the result of an ejection event from the Galactic disk forcing some stars to leave their place of birth as so-called runaway stars. Here, we present a detailed spectroscopic and kinematic analysis of the runaway B star HIP 60350 to determine which runaway scenario—a supernova expl…
The Optical Companion to the Binary Millisecond Pulsar J1824-2452H in the Globular Cluster M28
Dalessandro, E.; Ransom, S. M.; Possenti, A. +8 more
We report on the optical identification of the companion star to the eclipsing millisecond pulsar (MSP) PSR J1824-2452H in the galactic globular cluster M28 (NGC 6626). This star is at only 0farcs2 from the nominal position of the pulsar and it shows optical variability (~0.25 mag) that nicely correlates with the pulsar orbital period. It is locat…
A Comparison of Hard X-ray Photon Indices and Iron Kα Emission Lines in X-ray Luminous Narrow- and Broad-line Seyfert 1 Galaxies
Zhang, Shuang-Nan; Zhou, Xin-Lin
We use publicly available XMM-Newton data to systematically compare the hard X-ray photon indices, Γ2-10 keV , and the iron Kα emission lines of narrow- and broad-line Seyfert 1 (NLS1 and BLS1) galaxies. We compile a flux-limited (f 2-10 keV >= 1 × 10-12 erg s-1 cm-2) sample including 114 …
A Unified Timing and Spectral Model for the Anomalous X-ray Pulsars XTE J1810-197 and CXOU J164710.2-455216
Stella, L.; Israel, G. L.; Zane, S. +3 more
Anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) are two small classes of X-ray sources strongly suspected to host a magnetar, i.e., an ultra-magnetized neutron star with B ≈ 1014-1015 G. Many SGRs/AXPs are known to be variable, and recently the existence of genuinely "transient" magnetars was discovered. Here, …
Atomic and Molecular Carbon as a Tracer of Translucent Clouds
Jenkins, Edward B.; France, Kevin; Burgh, Eric B.
Using archival, high-resolution far-ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra of 34 Galactic O and B stars, we measure C I column densities and compare them with measurements from the literature of CO and H2 with regard to understanding the presence of translucent clouds along the line of sight. We …
M/LB and Color Evolution for a Deep Sample of M sstarf Cluster Galaxies at z ~ 1: The Formation Epoch and the Tilt of the Fundamental Plane
Kelson, D. D.; van der Wel, A.; Illingworth, G. D. +2 more
We have measured velocity dispersions (σ) for a sample of 36 galaxies with J < 21.2 or Mr < -20.6 mag in MS 1054-03, a massive cluster of galaxies at z = 0.83. Our data are of uniformly high quality down to our selection limit, our 16 hr exposures typically yielding errors of only δ(σ) ~ 10% for L* and fainter galaxies. By combini…
Cosmic-ray Acceleration Efficiency versus Temperature Equilibration: The Case of SNR 0509-67.5
Vink, J.; Kosenko, D.; Helder, E. A.
We study the 0509-67.5 supernova remnant in the Large Magellanic Cloud with the VLT/FORS2 spectrograph. We detect a broad component in the Hα emission with an FWHM of 2680 ± 70 km s-1 and 3900 ± 800 km s-1 for the southwest (SW) and northeast (NE) shocks, respectively. For the SW, the proton temperature appears to be too low …
Testing Models for Molecular Gas Formation in Galaxies: Hydrostatic Pressure or Gas and Dust Shielding?
Hunt, Leslie K.; Fumagalli, Michele; Krumholz, Mark R.
Stars in galaxies form in giant molecular clouds that coalesce when the atomic hydrogen is converted into molecules. There are currently two dominant models based on the property of the galactic disk that determines its molecular fraction: either hydrostatic pressure driven by the gravity of gas and stars, or a combination of gas column density an…
Spitzer Mid-Infrared Spectroscopy of Compact Symmetric Objects: What Powers Radio-Loud Active Galactic Nuclei?
Perlman, Eric S.; Stocke, John T.; Darling, Jeremy +1 more
We present low- and high-resolution mid-infrared (mid-IR) spectra and photometry for eight compact symmetric objects (CSOs) taken with the Infrared Spectrograph on the Spitzer Space Telescope. The hosts of these young, powerful radio galaxies show significant diversity in their mid-IR spectra. This includes multiple atomic fine-structure lines, H<…