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A Window on the Earliest Star Formation: Extreme Photoionization Conditions of a High-ionization, Low-metallicity Lensed Galaxy at z ∼ 2*
Pettini, Max; Erb, Dawn K.; Brammer, Gabriel B. +2 more
We report new observations of SL2S J021737-051329, a lens system consisting of a bright arc at z = 1.84435, magnified ∼17× by a massive galaxy at z = 0.65. SL2S0217 is a low-mass (M < 109 M ⊙), low-metallicity (Z ∼ 1/20 Z ⊙) galaxy, with extreme star-forming conditions that produce strong nebular UV emission lin…
NICER and Fermi GBM Observations of the First Galactic Ultraluminous X-Ray Pulsar Swift J0243.6+6124
Remillard, Ronald A.; Chakrabarty, Deepto; Ray, Paul S. +20 more
Swift J0243.6+6124 is a newly discovered Galactic Be/X-ray binary, revealed in late 2017 September in a giant outburst with a peak luminosity of 2 × 1039(d/7 kpc)2 erg s-1 (0.1-10 keV), with no formerly reported activity. At this luminosity, Swift J0243.6+6124 is the first known galactic ultraluminous X-ray pulsar.…
Gaia-DR2 Confirms VLBA Parallaxes in Ophiuchus, Serpens, and Aquila
Kounkel, Marina; Rodríguez, Luis F.; Loinard, Laurent +9 more
We present Gaia-DR2 astrometry of a sample of YSO candidates in Ophiuchus, Serpens Main, and Serpens South/W40 in the Aquila Rift, which had been mainly identified by their infrared excess with Spitzer. We compare the Gaia-DR2 parallaxes against published and new parallaxes obtained from our Very Long Baseline Array (VLBA) program Gould’s Belt Dis…
The MOSDEF Survey: Direct Observational Constraints on the Ionizing Photon Production Efficiency, ξ ion, at z ∼ 2
Siana, Brian; Shapley, Alice E.; Reddy, Naveen A. +11 more
We combine Hα and Hβ spectroscopic measurements and UV photometry for a sample of 673 galaxies from the MOSDEF survey to constrain hydrogen-ionizing photon production efficiencies ({ξ }ion}) at z = 1.4-2.6. We find < {log}({ξ }ion}/[{{{s}}}-1/{erg} {{{s}}}-1 {Hz}}-1])> = 25.06 (25.34), a…
The bright-star masks for the HSC-SSP survey
Oguri, Masamune; Medezinski, Elinor; Bosch, James +4 more
We present the procedure to build and validate the bright-star masks for the Hyper-Suprime-Cam Strategic Subaru Proposal (HSC-SSP) survey. To identify and mask the saturated stars in the full HSC-SSP footprint, we rely on the Gaia and Tycho-2 star catalogues. We first assemble a pure star catalogue down to GGaia < 18 after removing ∼…
Surface clay formation during short-term warmer and wetter conditions on a largely cold ancient Mars
Michalski, Joseph R.; Bishop, Janice L.; Fairén, Alberto G. +5 more
The ancient rock record for Mars has long been at odds with climate modelling. The presence of valley networks, dendritic channels and deltas on ancient terrains points towards running water and fluvial erosion on early Mars1, but climate modelling indicates that long-term warm conditions were not sustainable2. Widespread phy…
Spectra of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
Ellis, Richard; Filippenko, Alexei V.; Pan, Yen-Chen +20 more
Most Type I superluminous supernovae (SLSNe-I) reported to date have been identified by their high peak luminosities and spectra lacking obvious signs of hydrogen. We demonstrate that these events can be distinguished from normal-luminosity SNe (including Type Ic events) solely from their spectra over a wide range of light-curve phases. We use thi…
Age Determinations of the Hyades, Praesepe, and Pleiades via MESA Models with Rotation
Choi, Jieun; Conroy, Charlie; Dotter, Aaron +4 more
The Hyades, Praesepe, and Pleiades are well-studied stellar clusters that anchor important secondary stellar age indicators. Recent studies have shown that main sequence turn off based ages for these clusters may depend on the degree of rotation in the underlying stellar models. Rotation induces structural instabilities that can enhance the chemic…
A white dwarf catalogue from Gaia-DR2 and the Virtual Observatory
Solano, E.; Rebassa-Mansergas, A.; Torres, S. +4 more
We present a catalogue of 73 221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia-DR2 catalogue. White dwarfs were selected from the Gaia Hertzsprung-Russell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all whi…
The escape speed curve of the Galaxy obtained from Gaia DR2 implies a heavy Milky Way
Anders, F.; Chiappini, C.; Steinmetz, M. +6 more
We measure the escape speed curve of the Milky Way based on the analysis of the velocity distribution of 2850 counter-rotating halo stars from the Gaia Data Release 2. The distances were estimated through the StarHorse code, and only stars with distance errors smaller than 10% were used in the study. The escape speed curve is measured at Galactoce…