Astro Coffee

Suggested papers for
Tue, Sep 19, 2017 at 11 am
Thu, Sep 21, 2017 at 2 pm
Fri, Sep 22, 2017 at 11 am

16 Sep 2017

Accreting black hole binaries in globular clusters

We explore the formation of mass-transferring binary systems containing black holes within globular clusters. We show that it is possible to form mass-transferring black hole binaries with main sequence, giant, and white dwarf companions with a variety of orbital parameters in globular clusters spanning a large range in present-day properties. All mass-transferring black hole binaries found in our models at late times are dynamically created. The black holes in these systems experienced a media...

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15 Sep 2017

Binary stars in the Galactic thick disc

The combination of asteroseismologically-measured masses with abundances from detailed analyses of stellar atmospheres challenges our fundamental knowledge of stars and our ability to model them. Ancient red-giant stars in the Galactic thick disc are proving to be most troublesome in this regard. They are older than 5 Gyr, a lifetime corresponding to an initial stellar mass of about $1.2{\mathrm{M}_{\odot}}$. So why do the masses of a sizeable fraction of thick-disc stars exceed $1.3{\mathrm{M}...

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13 Sep 2017

Stochastic modeling of multiwavelength variability of the classical BL Lac object OJ 287 on timescales ranging from decades to hours

We present the results of our power spectral analysis for the BL Lac object OJ 287, utilizing the Fermi-LAT survey at high-energy gamma-rays, the Swift-XRT data in X-rays, several ground-based telescopes and the Kepler satellite in optical, and single-dish GHz-band radio telescopes. The multiwavelength light curves of the source are modeled in terms of a continuous-time auto regressive moving average (CARMA) process. Due to the inclusion of the Kepler data, we were able to construct for the fir...

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15 Sep 2017

Kronos & Krios: Evidence for accretion of a massive, rocky planetary system in a comoving pair of solar-type stars

We report and discuss the discovery of a comoving pair of bright solar-type stars, HD 240430 and HD 240429, with a significant difference in their chemical abundances. The two stars have an estimated 3D separation of $\approx 0.6$ pc ($\approx 0.01$ pc projected) at a distance of $r\approx 100$ pc with nearly identical three-dimensional velocities, as inferred from Gaia TGAS parallaxes and proper motions, and high-precision radial velocity measurements. Stellar parameters determined from high-r...

19 Sep 2017

ALMA reveals metals yet no dust within multiple components in CR7

We present spectroscopic follow-up observations of CR7 with ALMA, targeted at constraining the infrared (IR) continuum and [CII]$_{158 \mu \rm m}$ line-emission at high spatial resolution matched to the HST/WFC3 imaging. CR7 is a luminous Ly$\alpha$ emitting galaxy at $z=6.6$ that consists of three separated UV-continuum components. Our observations reveal several well-separated components of [CII] emission. The two most luminous components in [CII] coincide with the brightest UV components (A ...

18 Sep 2017

A candidate sub-parsec binary black hole in the Seyfert galaxy NGC 7674

P. Kharb, D. V. Lal, D. Merritt

The existence of binary supermassive black holes (SBHs) is predicted by models of hierarchical galaxy formation. To date, only a single binary SBH has been imaged, at a projected separation of 7.3 pc. Here, we report the detection of a candidate dual SBH with projected separation of 0.35 pc in the gas-rich interacting spiral galaxy NGC 7674 (Mrk 533). This peculiar Seyfert galaxy possesses a roughly 0.7 kpc Z-shaped radio jet. The leading model for the formation of such sources postu...

14 Sep 2017

Investigating the Binarity of S0-2: Implications for its Origins and Robustness as a Probe of the Laws of Gravity around a Supermassive Black Hole

The star, S0-2, which orbits the supermassive black hole in our Galaxy with a period of 16 years, provides the strongest constraint on both the mass of the black hole and the distance to the Galactic center. S0-2 will soon also provide the first measurement of relativistic effects near a supermassive black hole. In this work, we report the first limits on the binarity of S0-2 from radial velocity monitoring, which has implications for both understanding its origin as well as its robustness as a...

19 Sep 2017

Understanding substructure in the SSA22 protocluster region using cosmological simulations

We investigate the nature and evolution of substructure within the SSA22 protocluster region at $z=3.09$ using cosmological simulations. A redshift histogram constructed from current spectroscopic observations of the SSA22 protocluster reveals two separate peaks at $z = 3.065$ (blue) and $z = 3.095$ (red). Based on these data, we report updated overdensity and mass calculations for the SSA22 protocluster. We find $\delta_{b,gal}=4.8 \pm 1.8$, $\delta_{r,gal}=9.5 \pm 2.0$ for the blue and red pe...

18 Sep 2017

Probing large scale coherence between Spitzer IR and Chandra X-ray source-subtracted cosmic backgrounds

We present new measurements of the large scale clustering component of the cross-power spectra of the source-subtracted Spitzer-IRAC Cosmic Infrared Background (CIB) and Chandra-ACIS Cosmic X-ray Background (CXB) surface brightness fluctuations. Our investigation uses data from the Chandra Deep Field South (CDFS), Hubble Deep Field North (HDFN), EGS/AEGIS field and UDS/SXDF surveys, comprising 1160 Spitzer hours and $\sim$ 12 Ms of Chandra data collected over a total area of 0.3 deg$^2$. We rep...

24 Jul 2017

VLBA imaging of the 3mm SiO maser emission in the disk-wind from the massive protostellar system Orion Source I

We present the first images of the 28SiO v=1, J=2-1 maser emission around the closest known massive young stellar object Orion Source I observed at 86 GHz (3mm) with the VLBA. These images have high spatial (~0.3 mas) and spectral (~0.054 km/s) resolutions. We find that the 3mm masers lie in an X-shaped locus consisting of four arms, with blue-shifted emission in the south and east arms and red-shifted emission in the north and west arms. Comparisons with previous images of the 28SiO v=1,2, J=1...

Updated 2017/09/22 11:38:47