Search Publications
Spectral analysis of the extremely hot DA white dwarf PG 0948+534
Rauch, T.; Werner, K.; Reindl, N.
There is a striking paucity of hydrogen-rich (DA) white dwarfs (WDs) relative to their hydrogen-deficient (non-DA) counterparts at the very hot end of the WD cooling sequence. The three hottest known DAs (surface gravity log g ≥ 7.0) have effective temperatures around T_{eff} = 140 000 K, followed by only five objects in the range 104 000-120 000 …
The chemical structure of the very young starless core L1521E
Nagy, Z.; Caselli, P.; Spezzano, S. +5 more
Context. L1521E is a dense starless core in Taurus that was found to have relatively low molecular depletion by earlier studies, thus suggesting a recent formation.
Aims: We aim to characterize the chemical structure of L1521E and compare it to the more evolved L1544 pre-stellar core.
Methods: We have obtained 2.5 × 2.5 arcminute maps to…
A deep X-ray view of the bare AGN Ark 120. V. Spin determination from disc-Comptonisation efficiency method
Stern, D.; Farrah, D.; Done, C. +13 more
Context. The spin of supermassive black holes (SMBH) in active galactic nuclei (AGN) can be determined from spectral signature(s) of relativistic reflection such as the X-ray iron Kα line profile, but this can be rather uncertain when the line of sight intersects the so-called warm absorber and/or other wind components as these distort the continu…
The Swift UVOT Stars Survey. III. Photometry and Color-Magnitude Diagrams of 103 Galactic Open Clusters
Hagen, Lea M. Z.; Siegel, Michael H.; Porterfield, Blair L. +2 more
As part of the Swift/Ultraviolet-Optical Telescope Stars Survey, we present near-ultraviolet (NUV; 3000-1700 Å) point-source photometry for 103 Galactic open clusters. These data, taken over the span of the mission, provide a unique and unprecedented set of NUV point-source photometry on simple stellar populations. After applying a membership anal…
Greening of the brown-dwarf desert. EPIC 212036875b: a 51 MJ object in a 5-day orbit around an F7 V star
Cochran, William D.; Endl, Michael; Redfield, Seth +55 more
Context. Although more than 2000 brown dwarfs have been detected to date, mainly from direct imaging, their characterisation is difficult due to their faintness and model-dependent results. In the case of transiting brown dwarfs, however, it is possible to make direct high-precision observations.
Aims: Our aim is to investigate the nature and…
Discovery of an Intermediate-luminosity Red Transient in M51 and Its Likely Dust-obscured, Infrared-variable Progenitor
Williams, Robert E.; Kulkarni, S. R.; Tinyanont, Samaporn +49 more
We present the discovery of an optical transient (OT) in Messier 51, designated M51 OT2019-1 (also ZTF 19aadyppr, AT 2019abn, ATLAS19bzl), by the Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed luminosity of M r = -13 (νL ν = 9 × 106 L ⊙), in the luminosity gap between novae …
X-Ray Reprocessing: Through the Eclipse Spectra of High-mass X-Ray Binaries with XMM-Newton
Paul, Biswajit; Kretschmar, Peter; Aftab, Nafisa
The study of X-ray reprocessing is one of the key diagnostic tools to probe the environment in X-ray binary systems. One difficult aspect of studying X-ray reprocessing is the presence of much brighter primary radiation from the compact star together with the reprocessed radiation. In contrast, for eclipsing systems, the X-rays we receive during e…
Metal-poor Stars Observed with the Automated Planet Finder Telescope. II. Chemodynamical Analysis of Six Low-metallicity Stars in the Halo System of the Milky Way
Zhao, Gang; Placco, Vinicius M.; Li, Haining +2 more
In this work, we study the chemical compositions and kinematic properties of six metal-poor stars with [Fe/H] < -2.5 in the Galactic halo. From high-resolution (R ∼ 110,000) spectroscopic observations obtained with the Lick/Automated Planet Finder, we determined individual abundances for up to 23 elements, to quantitatively evaluate our sample.…
Transition from Circular-ribbon to Parallel-ribbon Flares Associated with a Bifurcated Magnetic Flux Rope
Ding, M. D.; Guo, Y.; Zhong, Z. +2 more
Magnetic flux ropes play a key role in triggering solar flares in the solar atmosphere. In this paper, we investigate the evolution of NOAA Active Region 12268 within 36 hr from 2015 January 29 to 30, during which a flux rope was formed and three M-class and three C-class flares were triggered without coronal mass ejections. During the evolution o…
Constraining Compact Object Formation with 2M0521
Breivik, Katelyn; Andrews, Jeff J.; Chatterjee, Sourav
We show that the recently discovered binary 2M05215658+4359220 (2M0521), comprising a giant star (GS) orbiting a suspected black hole (BH) in an ∼80 day orbit, may be instrumental in shedding light on uncertain BH-formation physics and can be a test case for studying wind accretion models. Using binary population synthesis with a realistic prescri…