Search Publications
The evolution of massive stars and their spectra. I. A non-rotating 60 M⊙ star from the zero-age main sequence to the pre-supernova stage
Meynet, Georges; Groh, Jose H.; Ekström, Sylvia +1 more
For the first time, the interior and spectroscopic evolution of a massive star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For this purpose, we combined stellar evolution models using the Geneva code and stellar atmospheric/wind models using CMFGEN. With our approach, we were able to produce observables, suc…
A library of near-infrared integral field spectra of young M-L dwarfs
Pinte, C.; Homeier, D.; Lagrange, A. -M. +5 more
Context. At young ages, low surface gravity affects the atmospheric properties of ultracool dwarfs. The impact on medium-resolution near-infrared (NIR) spectra has only been slightly investigated at the M-L transition so far.
Aims: We present a library of NIR (1.1-2.45 µm) medium-resolution (R ~ 1500-2000) integral field spectra of 15 y…
Mining circumgalactic baryons in the low-redshift universe
Chen, Hsiao-Wen; Liang, Cameron J.
This paper presents an absorption-line study of the multiphase circumgalactic medium (CGM) based on observations of Lyα, C II, C IV, Si II, Si III, and Si IV absorption transitions in the vicinities of 195 galaxies at redshift z < 0.176. The galaxy sample is established based on a cross-comparison between public galaxy and quasi-stellar object …
Extended Main Sequence Turnoffs in Intermediate-age Star Clusters: A Correlation between Turnoff Width and Early Escape Velocity
Girardi, Léo; Chandar, Rupali; Marigo, Paola +9 more
We present a color-magnitude diagram analysis of deep Hubble Space Telescope imaging of a mass-limited sample of 18 intermediate-age (1-2 Gyr old) star clusters in the Magellanic Clouds, including eight clusters for which new data were obtained. We find that all star clusters in our sample feature extended main-sequence turnoff (eMSTO) regions tha…
Unexpected variability of Martian hydrogen escape
Montmessin, Franck; Bertaux, Jean-Loup; Chaffin, Michael S. +3 more
Mars today is much drier than the Earth, though they likely began with similar relative amounts of water. One potential cause for this discrepancy is hydrogen loss to space, which may have removed a large fraction of Mars' initial water. Here we demonstrate an order-of-magnitude change in the Martian hydrogen escape rate in 2007, inconsistent with…
A Multi-Observatory Inter-Comparison of Line-of-Sight Synoptic Solar Magnetograms
Liu, Y.; Riley, P.; Hoeksema, T. +7 more
The observed photospheric magnetic field is a crucial parameter for understanding a range of fundamental solar and heliospheric phenomena. Synoptic maps, in particular, which are derived from the observed line-of-sight photospheric magnetic field and built up over a period of 27 days, are the main driver for global numerical models of the solar co…
Cosmological constraints on very dark photons
Fradette, Anthony; Pospelov, Maxim; Pradler, Josef +1 more
We explore the cosmological consequences of kinetically mixed dark photons with a mass between 1 MeV and 10 GeV and an effective electromagnetic fine structure constant as small as 10-38. We calculate the freeze-in abundance of these dark photons in the early universe and explore the impact of late decays on big bang nucleosynthesis and…
HST-COS Observations of AGNs. II. Extended Survey of Ultraviolet Composite Spectra from 159 Active Galactic Nuclei
Stevans, Matthew L.; Shull, J. Michael; Danforth, Charles W. +1 more
The ionizing fluxes from quasars and other active galactic nuclei (AGNs) are critical for interpreting their emission-line spectra and for photoionizing and heating the intergalactic medium. Using far-ultraviolet (FUV) spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we directly measure the rest-frame ionizin…
The origin of cold gas in giant elliptical galaxies and its role in fuelling radio-mode AGN feedback
Simionescu, A.; von der Linden, A.; Fabian, A. C. +12 more
The nature and origin of the cold interstellar medium (ISM) in early-type galaxies are still a matter of debate, and understanding the role of this component in galaxy evolution and in fuelling the central supermassive black holes requires more observational constraints. Here, we present a multiwavelength study of the ISM in eight nearby, X-ray an…
Predicting the Sun's Polar Magnetic Fields with a Surface Flux Transport Model
Hathaway, David H.; Upton, Lisa
The Sun's polar magnetic fields are directly related to solar cycle variability. The strength of the polar fields at the start (minimum) of a cycle determine the subsequent amplitude of that cycle. In addition, the polar field reversals at cycle maximum alter the propagation of galactic cosmic rays throughout the heliosphere in fundamental ways. W…