Astro Coffee

Suggested papers for
Tue, Apr 03, 2018, Thu, Apr 05, 2018, and Fri, Apr 06, 2018 at 11 am

4 Jan 2018

Star formation history of the Galactic bulge from deep HST imaging of low reddening windows

Despite the huge amount of photometric and spectroscopic efforts targetting the Galactic bulge over the past few years, its age distribution remains controversial owing to both the complexity of determining the age of individual stars and the difficult observing conditions. Taking advantage of the recent release of very deep, proper-motion-cleaned colour--magnitude diagrams (CMDs) of four low reddening windows obtained with the Hubble Space Telescope (HST), we used the CMD-fitting technique to ...

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5 Apr 2018

Recovering the systemic redshift of galaxies from their Lyman-alpha line profile

The Lyman alpha (lya) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km/s compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics and correlations with quasar absorption lines when only lya is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the lya line profile. We use spectroscopic observations of Lyman-Alph...

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28 Mar 2018

A galaxy lacking dark matter

Pieter van Dokkum, Shany Danieli, Yotam Cohen, Allison Merritt, + 7 more

Studies of galaxy surveys in the context of the cold dark matter paradigm have shown that the mass of the dark matter halo and the total stellar mass are coupled through a function that varies smoothly with mass. Their average ratioMhalo/Mstarshas a minimum of about 30 for galaxies with stellar masses near that of the Milky Way (approximately 5 × 1010solar masses) and increases both towards lower masses and towards higher masses1,2. The scatter in this relation is not well known; it is gene...

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2 Apr 2018

Progress on ELROI satellite license plate flight prototypes

The Extremely Low-Resource Optical Identifier (ELROI) beacon is a concept for a milliwatt optical "license plate" that can provide unique ID numbers for everything that goes into space. Using photon counting to enable extreme background rejection in real time, the ID number can be uniquely identified from the ground in a few minutes, even if the ground station detects only a few photons per second. The ELROI concept has been validated in long-range ground tests, and orbital prototypes are sched...

20 Mar 2018

Tycho-B: an unlikely companion for SN 1572

If some or all Type Ia SNe arise from accretion onto a massive WD from a companion, then the companion will remain in some form after the SN explosion. Tycho-B is an unusual, relatively hot star along the line of sight to Tycho's SNR -- conclusively shown to be a Type Ia -- and has been suggested as such a companion. If the interior of Tycho's SNR contains unshocked Fe, and if Tycho-B is either within the SNR shell or in the background, then one might hope to see evidence of this in the UV spec...

2 Apr 2018

New Y and T dwarfs from WISE identified by Methane Imaging

We identify new Y- and T-type brown dwarfs from the WISE All Sky data release using images obtained in filters that divide the traditional near-infrared H and J bands into two halves -- specifically CH4s & CH4l in the H and J2 & J3 in the J. This proves to be very effective at identifying cool brown dwarfs via the detection of their methane absorption, as well as providing preliminary classification using methane colours and WISE-to-near-infrared colours. New and updated calibrations be...

4 Apr 2018

The Standard Model of Cosmology: A Skeptic's Guide

The status of the standard cosmological model, also known as "LCDM" is described. With some simple assumptions, this model fits a wide range of data, with just six (or seven) free parameters. One should be skeptical about this claim, since it implies that we now have an astonishingly good picture of the statistical properties of the large-scale Universe. However, the successes of the model cannot be denied, including more than 1000 sigma worth of detection of CMB anisotropy power. The model is ...

4 Apr 2018

On the nature of the black-body stars

We study the physical nature of the black-body stars recently discovered. We use sets of white dwarf (WD) model atmospheres with pure-He, pure-H, and H/He mixtures to compute synthetic spectra and compare theoretical expectations with observations of the black-body stars. We find that the spectral properties of the black-body stars in the UV and the optical are reproduced to high-accuracy by helium dominated atmospheres possibly with trace amounts of hydrogen below the spectroscopic detection l...

04 Apr 2018

A density cusp of quiescent X-ray binaries in the central parsec of the Galaxy

Charles J. Hailey, Kaya Mori, Franz E. Bauer, Michael E. Berkowitz, + 1 more

The existence of a ‘density cusp’1,2—a localized increase in number—of stellar-mass black holes near a supermassive black hole is a fundamental prediction of galactic stellar dynamics3. The best place to detect such a cusp is in the Galactic Centre, where the nearest supermassive black hole, Sagittarius A*, resides. As many as 20,000 black holes are predicted to settle into the central parsec of the Galaxy as a result of dynamical friction3,4,5; however, so far no density cusp of black h...

Updated 2018/04/06 11:25:18

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