Search Publications
An HST Survey of Protostellar Outflow Cavities: Does Feedback Clear Envelopes?
Manoj, P.; Kounkel, Marina; Pokhrel, Riwaj +10 more
We study protostellar envelope and outflow evolution using Hubble Space Telescope NICMOS or WFC3 images of 304 protostars in the Orion molecular clouds. These near-IR images resolve structures in the envelopes delineated by the scattered light of the central protostars with 80 au resolution, and they complement the 1.2 µm to 870 µm spe…
Energetic Electron Distribution of the Coronal Acceleration Region: First Results from Joint Microwave and Hard X-Ray Imaging Spectroscopy
Krucker, Säm; Reeves, Katharine K.; Chen, Bin +2 more
Nonthermal sources located above bright flare arcades, referred to as the "above-the-loop-top" sources, have been often suggested as the primary electron acceleration site in major solar flares. The X8.2 limb flare on 2017 September 10 features such an above-the-loop-top source, which was observed in both microwaves and hard X-rays (HXRs) by the E…
The MOSDEF Survey: Environmental Dependence of the Gas-phase Metallicity of Galaxies at 1.4 ≤ z ≤ 2.6
Barro, Guillermo; Siana, Brian; Shapley, Alice E. +13 more
Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field survey, we investigate the role of the local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical…
The Compact UV Size of Green Pea Galaxies As Local Analogs of High-redshift Lyα-Emitters
Kim, Keunho J.; Malhotra, Sangeeta; Yang, Huan +1 more
We study the dependence of Lyα escape from galaxies on UV continuum size and luminosity using a sample of 40 Green Pea (GP) galaxies, which are the best local analogs of high-redshift Lyα emitters (LAEs). We use the Cosmic Origins Spectrograph near-ultraviolet images from the Hubble Space Telescope to measure the UV size and luminosity with 0"047 …
The Luminosity Function of Bright QSOs at z ∼ 4 and Implications for the Cosmic Ionizing Background
Grazian, Andrea; Boutsia, Konstantina; Cupani, Guido +8 more
Based on results by recent surveys, the number of bright quasars at redshifts z > 3 is being constantly revised upward. The current consensus is that at bright magnitudes (M1450 ≤ -27) the number densities of such sources could have been underestimated by a factor of 30%-40%. In the framework of the QUBRICS survey, we identified 58 b…
ZTFJ0038+2030: A Long-period Eclipsing White Dwarf and a Substellar Companion
Kulkarni, S. R.; Bell, Keaton J.; Riddle, Reed +12 more
In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with an orbital period of 10.4 hr and an undetected substellar companion. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of 0.50 ± 0.02 M⊙…
Infrared Excesses Around Bright White Dwarfs from Gaia and unWISE. II
Lai, Samuel; Rebassa-Mansergas, Alberto; Xu, Siyi +7 more
Infrared excesses around white dwarf stars indicate the presence of various astrophysical objects of interest, including companions and debris disks. In this second paper of a series, we present follow-up observations of infrared excess candidates from Gaia and unWISE discussed in the first paper, Paper I. We report space-based infrared photometry…
HAZMAT. VII. The Evolution of Ultraviolet Emission with Age and Rotation for Early M Dwarf Stars
Loyd, R. O. Parke; Jackman, James A. G.; Peacock, Sarah +6 more
The ultraviolet (UV) emission from the most numerous stars in the universe, M dwarfs, impacts the formation, chemistry, atmospheric stability, and surface habitability of their planets. We have analyzed the spectral evolution of UV emission from M0-M2.5 (0.3-0.6 M⊙) stars as a function of age, rotation, and Rossby number using Hubble Sp…
Supervirial Temperature or Neon Overabundance? Suzaku Observations of the Milky Way Circumgalactic Medium
Nicastro, Fabrizio; Mathur, Smita; Gupta, Anjali +4 more
We analyzed Suzaku and Chandra observations of the soft diffuse X-ray background toward four sight lines with the goal of characterizing the X-ray emission from the Milky Way circumgalactic medium (CGM). We identified two thermal components of the CGM, one at a uniform temperature of kT = 0.176 ± 0.008 keV and the other at temperatures in the rang…
The Flattening Metallicity Gradient in the Milky Way's Thin Disk
Shen, Juntai; Li, Zhao-Yu; Vickers, John J.
We calculate the ages, orbits and phase-space coordinates for a sample of ~4 million LAMOST and Gaia stars. The ages are cross-matched and compared with values from two other popular age catalogs, which derive the ages using different methods. Of these ~4 million stars, we select a sample of 1.3 million stars and investigate their radial metallici…