Astro Coffee

Suggested papers for
Tue, May 03, 2016 at 03:00 PM and Thu, May 05, 2016 at 02:00 PM

26 Apr 2016

Magnetic cycles at different ages of stars

We study the different patterns of interannual magnetic variability in stars on or near the lower main sequence, approximately solar-type (G-K dwarf) stars in time series of 36 years from the Mount Wilson Observatory Ca\,{\sc ii}\,H\&K survey. Our main aim is to search for correlations between cycles, activity measures and ages. Time-frequency analysis has been used to discern and reveal patterns and morphology of stellar activity cycles, including multiple and changing cycles, in the datas...

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21 Apr 2016

Surface density effects in quenching: cause or effect?

There are very strong observed correlations between the specific star-formation rates (sSFR) of galaxies and their mean surface mass densities, {\Sigma}, as well as other aspects of their internal structure. These strong correlations have often been taken to indicate that the internal structure of a galaxy must play a major physical role, directly or indirectly, in the control of star-formation. In this paper we show by means of a very simple toy model that these correlations can arise naturall...

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22 Apr 2016

Directly Observing the Galaxies Likely Responsible for Reionization

We report a new analysis of the Hubble Frontier Fields clusters Abell 2744 and MACS 0416 using wavelet decomposition to remove the cluster light, enabling the detection of highly magnified (>50x) galaxies a factor of 10x fainter in luminosity than previous studies. We find 167 galaxies at z > 6, and with this sample we are able to characterize the UV luminosity function to M_UV = -12.5 at z ~ 6, -14 at z ~ 7 and -15 at z ~ 8. We find a steep faint-end slope (alpha <-2), and with our im...

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21 Apr 2016

The wind nebula around magnetar Swift J1834.9-0846

We report on the analysis of two deep XMM-Newton observations of the magnetar Swift J1834.9-0846 and its surrounding extended emission taken in March 2014 and October 2014, 2.5 and 3.1 years after the source went into outburst. The magnetar is only weakly detected in the first observation with an absorption corrected flux $F_{\rm 0.5-10 keV}\approx4\times10^{-14}$ erg s$^{-1}$ cm$^{-2}$, and a $3\sigma$ upper limit during the second observation of about $3\times10^{-14}$ erg s$^{-1}$ cm$^{-2}$....

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22 Apr 2016

Generalized Lomb-Scargle periodogram analysis of Super-Kamiokande and Sudbury Neutrino Observatory solar neutrino datasets

We apply the generalized Lomb-Scargle (LS) periodogram proposed by Zechmeister and Kurster, to the solar neutrino data from Super-Kamiokande (Super-K) using data from its first five years, and to Sudbury Neutrino Observatory (SNO) on data from both its salt and $\mathrm{D_2O}$ phases, in order to detect periodicities in these datasets. For each peak in the LS periodogram, we evaluate the statistical significance in two different ways. The first method involves calculating the False Alarm Probab...

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20 Apr 2016

The crucial role of higher-order multiplicity in wide binary formation: A case study using the $β$-Pictoris moving group

The "in-situ" formation of very wide binaries is hard to explain as their physical separations are beyond the typical size of a collapsing cloud core ($\approx$5000-10,000 au). Here we investigate the formation process of such systems. We compute population statistics such as the multiplicity fraction (MF), companion-star fraction (CSF) and physical separation distribution of companions in the $\beta$-Pictoris moving group (BPMG). We compare previous multiplicity studies in younger and older re...

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4 May 2016

An Empirical Determination of the Intergalactic Background Light from UV to FIR Wavelengths Using FIR Deep Galaxy Surveys and the Gamma-ray Opacity of the Universe

We have previously calculated the intergalactic background light (IBL) as a function of redshift in the far ultraviolet to near infrared range, based purely on data from deep galaxy surveys. Here we utilize similar methods to determine the mid- and far infrared IBL out to a wavelength of 850 microns. Our approach enables us to constrain the range of photon densities, based on the uncertainties from observationally determined luminosity densities and colors. By also including the effect of the 2...

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26 Apr 2016

High-velocity OH megamasers in IRAS 20100-4156: Evidence for a Supermassive Black Hole

We report the discovery of new, high-velocity narrow-line components of the OH megamaser in IRAS 20100-4156. Results from the Australian Square Kilometre Array Pathfinder (ASKAP)'s Boolardy Engineering Test Array (BETA) and the Australia Telescope Compact Array (ATCA) provide two independent measurements of the OH megamaser spectrum. We found evidence for OH megamaser clumps at $-$409 and $-$562 km/s (blue-shifted) from the systemic velocity of the galaxy, in addition to the lines previously kn...

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2 May 2016

Monitoring the Galactic Centre with Australia Telescope Compact Array

The supermassive black hole, Sagittarius A* (Sgr A*), at the centre of the Milky Way undergoes regular flaring activity which is thought to arise from the innermost region of the accretion flow. We performed the monitoring observations of the Galactic Centre to study the flux-density variations at 3mm using the Australia Telescope Compact Array (ATCA) between 2010 and 2014. We obtain the light curves of Sgr A* by subtracting the contributions from the extended emission around it, and the elevat...

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1 May 2016

The first low-mass black hole X-ray binary identified in quiescence outside of a globular cluster

The observed relation between the X-ray and radio properties of low-luminosity accreting black holes has enabled the identification of multiple candidate black hole X-ray binaries (BHXBs) in globular clusters. Here we report an identification of the radio source VLA J213002.08+120904 (aka M15 S2), recently reported in Kirsten et al. 2014, as a BHXB candidate. They showed that the parallax of this flat-spectrum variable radio source indicates a 2.2$^{+0.5}_{-0.3}$ kpc distance, which identifies ...

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28 Apr 2016

Are Some Milky Way Globular Clusters Hosted by Undiscovered Galaxies?

The confirmation of a globular cluster (GC) in the recently discovered ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question posed in the title. After estimating the halo mass of Eri II using a published stellar mass - halo mass relation, the one GC in this galaxy supports extending the relationship between the number of GCs hosted by a galaxy and the galaxy's total mass about two orders of magnitude in stellar mass below the previous limit. For this empirically determined...

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25 Apr 2016

Precision Stellar Astrophysics in the Kepler Era

The study of fundamental properties (such as temperatures, radii, masses, and ages) and interior processes (such as convection and angular momentum transport) of stars has implications on various topics in astrophysics, ranging from the evolution of galaxies to understanding exoplanets. In this contribution I will review the basic principles of two key observational methods for constraining fundamental and interior properties of single field stars: the study stellar oscillations (asteroseismolo...

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27 Apr 2016

A Distant Echo of Milky Way Central Activity closes the Galaxy's Baryon Census

We report on the presence of large amounts of million-degree gas in the Milky Way's interstellar and circum-galactic medium. This gas (1) permeates both the Galactic plane and the halo, (2) extends to distances larger than 60-200 kpc from the center, and (3) its mass is sufficient to close the Galaxy's baryon census.

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28 Apr 2016

The Galactic Center: A PeV Cosmic Ray Acceleration Factory

In this work, we propose that the cosmic rays are accelerated up to >PeV in galactic center. The interaction between cosmic rays and molecular clouds is responsible for the multi-TeV gamma-ray emissions for both the point source and diffuse one today. Enhanced by the small volume filling factor of the clumpy structure, the absorption of the gamma-rays leads to a sharp cut-off spectrum at tens of TeV produced in galactic center. Away from GC, the volume filling factor grows up and the absorpt...

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28 Apr 2016

Are Some Milky Way Globular Clusters Hosted by Undiscovered Galaxies?

The confirmation of a globular cluster (GC) in the recently discovered ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question posed in the title. After estimating the halo mass of Eri II using a published stellar mass - halo mass relation, the one GC in this galaxy supports extending the relationship between the number of GCs hosted by a galaxy and the galaxy's total mass about two orders of magnitude in stellar mass below the previous limit. For this empirically determined...

28 Apr 2016

Deep imaging of Eridanus II and its lone star cluster

We present deep imaging of the most distant dwarf discovered by the Dark Energy Survey, Eridanus II (Eri II). Our Magellan/Megacam stellar photometry reaches $\sim$$3$ mag deeper than previous work, and allows us to confirm the presence of a stellar cluster whose position is consistent with Eri II's center. This makes Eri II, at $M_V=-7.1$, the least luminous galaxy known to host a (possibly central) cluster. The cluster is partially resolved, and at $M_V=-3.5$ it accounts for $\sim$$4\%$ of Er...

3 May 2016

Orbital and physical parameters, and the distance of the eclipsing binary system OGLE-LMC-ECL-25658 in the Large Magellanic Cloud

We present an analysis of a new detached eclipsing binary, OGLE-LMC-ECL-25658, in the Large Magellanic Cloud. The system consists of two late G-type giant stars on an eccentric orbit and orbital period of ~200 days. The system shows total eclipses and the components have similar temperatures, making it ideal for a precise distance determination. Using multi-color photometric and high resolution spectroscopic data, we have performed an analysis of light and radial velocity curves simultaneously ...

4 May 2016

Measurement of the Black Hole Mass in NGC 1332 from ALMA Observations at 0.044 Arcsecond Resolution

We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 3 observations of CO(2-1) emission from the circumnuclear disk in the E/S0 galaxy NGC 1332 at 0.044" resolution. The disk exhibits regular rotational kinematics and central high-velocity emission (+/-500 km/s) consistent with the presence of a compact central mass. We construct models for a thin, dynamically cold disk in the gravitational potential of the host galaxy and black hole, and fit the beam-smeared model line profiles...

21 Apr 2016

The Evolution of Normal Galaxy X-ray Emission Through Cosmic History: Constraints from the 6 Ms Chandra Deep Field-South

We present measurements of the evolution of normal-galaxy X-ray emission from $z \approx$ 0-7 using local galaxies and galaxy samples in the 6 Ms Chandra Deep Field-South (CDF-S) survey. The majority of the CDF-S galaxies are observed at rest-frame energies above 2 keV, where the emission is expected to be dominated by X-ray binary (XRB) populations; however, hot gas is expected to provide small contributions to the observed- frame < 1 keV emission at $z < 1$. We show that a single scalin...

20 Apr 2016

Hello Darkness My Old Friend: The Fading of the Nearby TDE ASASSN-14ae

We present late-time optical spectroscopy taken with the Large Binocular Telescope's Multi-Object Double Spectrograph, an improved ASAS-SN pre-discovery non-detection, and late-time SWIFT observations of the nearby ($d=193$ Mpc, $z=0.0436$) tidal disruption event (TDE) ASASSN-14ae. Our observations span from $\sim$20 days before to $\sim$750 days after discovery. The proximity of ASASSN-14ae allows us to study the optical evolution of the flare and the transition to a host dominated state with ...

2 May 2016

Kepler K2 Observations of Sco X-1: Orbital Modulations and Correlations with Fermi GBM and MAXI

We present a multi-wavelength study of the low-mass X-ray binary Sco X-1 using Kepler K2 optical data and Fermi GBM and MAXI X-ray data. We recover a clear sinusoidal orbital modulation from the Kepler data. Optical fluxes are distributed bimodally around the mean orbital light curve, with both high and low states showing the same modulation. The high state is broadly consistent with the flaring branch of the Z diagram and the low state with the normal branch. We see both rapid optical flares a...


Updated 2016/05/05 14:54:02

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