arXiv subjects

Daniel Huber

Publications and source records attributed to Daniel Huber.

At least 253 records · Page 14Linked to original sources

arXiv2017

The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars

(Abridged) We present the first APOKASC catalog of spectroscopic and asteroseismic data for 415 dwarfs and subgiants. Asteroseismic data have been obtained by Kepler in short cadence. The spectroscopic parameters are based on spectra taken as part of APOGEE and correspond to DR13 of SDSS. We analyze our data using two Teff scales, the spectroscopic values from DR13 and those derived from SDSS griz photometry. We use the differences in our results arising from these choices as a test of systematic Teff, and find that they can lead to significant differences in the derived stellar properties. Determinations of surface gravity ($\log{g}$), mean density ($ρ$), radius ($R$), mass ($M$), and age ($τ$) for the whole sample have been carried out with stellar grid-based modeling. We have assessed random and systematic error sources in the spectroscopic and seismic data, as well as in the grid-based modeling determination of the stellar quantities in the catalog. We provide stellar properties for both Teff scales. The median combined (random and systematic) uncertainties are 2% (0.01 dex; $\log{g}$), 3.4% ($ρ$), 2.6% ($R$), 5.1% ($M$), and 19% ($τ$) for the photometric Teff scale and 2% ($\log{g}$), 3.5% ($ρ$), 2.7% ($R$), 6.3% ($M$), and 23% ($τ$) for the spectroscopic scale. Comparisons with stellar quantities in the catalog by Chaplin et al.(2014) highlight the importance of metallicity measurements for determining stellar parameters accurately. We compare our results with those from other sources, including stellar radii determined from TGAS parallaxes and asteroseismic analyses based on individual frequencies. We find a very good agreement in all cases. Comparisons give strong support to the determination of stellar quantities based on global seismology, a relevant result for future missions such as TESS and PLATO. Table 5 corrected (wrongly listed SDSS Teff before).

astro-ph.SR↗

arXiv2017

Seeing double with K2: Testing re-inflation with two remarkably similar planets around red giant branch stars

Despite more than 20 years since the discovery of the first gas giant planet with an anomalously large radius, the mechanism for planet inflation remains unknown. Here, we report the discovery of EPIC228754001.01, an inflated gas giant planet found with the NASA K2 Mission, and a revised mass for another inflated planet, K2-97b. These planets reside on ~9 day orbits around host stars which recently evolved into red giants. We constrain the irradiation history of these planets using models constrained by asteroseismology and Keck/HIRES spectroscopy and radial velocity measurements. We measure planet radii of 1.31 +\- 0.11 Rjup and and 1.30 +\- 0.07 Rjup, respectively. These radii are typical for planets receiving the current irradiation, but not the former, zero age main sequence irradiation of these planets. This suggests that the current sizes of these planets are directly correlated to their current irradiation. Our precise constraints of the masses and radii of the stars and planets in these systems allow us to constrain the planetary heating efficiency of both systems as 0.03% +0.03%/-0.02%. These results are consistent with a planet re-inflation scenario, but suggest the efficiency of planet re-inflation may be lower than previously theorized. Finally, we discuss the agreement within 10% of stellar masses and radii, and planet masses, radii, and orbital periods of both systems and speculate that this may be due to selection bias in searching for planets around evolved stars.

astro-ph.EP↗

arXiv2017

The TESS-HERMES survey Data Release 1: high-resolution spectroscopy of the TESS southern continuous viewing zone

The Transiting Exoplanet Survey Satellite (TESS) will provide high precision time-series photometry for millions of stars with at least a half-hour cadence. Of particular interest are the circular regions of 12-degree radius centered around the ecliptic poles that will be observed continuously for a full year. Spectroscopic stellar parameters are desirable to characterize and select suitable targets for TESS, whether they are focused on exploring exoplanets, stellar astrophysics, or Galactic archaeology. Here, we present spectroscopic stellar parameters ($T_{\rm eff}$, $\log g$, [Fe/H], $v \sin i$, $v_{\rm micro}$) for about 16,000 dwarf and subgiant stars in TESS' southern continuous viewing zone. For almost all the stars, we also present Bayesian estimates of stellar properties including distance, extinction, mass, radius, and age using theoretical isochrones. Stellar surface gravity and radius are made available for an additional set of roughly 8,500 red giants. All our target stars are in the range $10<V<13.1$. Among them, we identify and list 227 stars belonging to the Large Magellanic Cloud. The data were taken using the the High Efficiency and Resolution Multi-Element Spectrograph (HERMES, R $\sim 28,000$) at the Anglo-Australian Telescope as part of the TESS-HERMES survey. Comparing our results with the TESS Input Catalog (TIC) shows that the TIC is generally efficient in separating dwarfs and giants, but it has flagged more than hundred cool dwarfs ($T_{\rm eff}< 4800$ K) as giants, which ought to be high-priority targets for the exoplanet search. The catalog can be accessed via http://www.physics.usyd.edu.au/tess-hermes/ , or at MAST via https://archive.stsci.edu/prepds/tess-hermes/ .

astro-ph.SR↗

arXiv2017

The masses of retired A stars with asteroseismology: Kepler and K2 observations of exoplanet hosts

We investigate the masses of "retired A stars" using asteroseismic detections on seven low-luminosity red-giant and sub-giant stars observed by the NASA Kepler and K2 Missions. Our aim is to explore whether masses derived from spectroscopy and isochrone fitting may have been systematically overestimated. Our targets have all previously been subject to long term radial velocity observations to detect orbiting bodies, and satisfy the criteria used by Johnson et al. (2006) to select survey stars that may have had A-type (or early F-type) main-sequence progenitors. The sample actually spans a somewhat wider range in mass, from $\approx 1\,\rm M_{\odot}$ up to $\approx 1.7\,\rm M_{\odot}$. Whilst for five of the seven stars the reported discovery mass from spectroscopy exceeds the mass estimated using asteroseismology, there is no strong evidence for a significant, systematic bias across the sample. Moreover, comparisons with other masses from the literature show that the absolute scale of any differences is highly sensitive to the chosen reference literature mass, with the scatter between different literature masses significantly larger than reported error bars. We find that any mass difference can be explained through use of differing constraints during the recovery process. We also conclude that underestimated uncertainties on the input parameters can significantly bias the recovered stellar masses, which may have contributed to the controversy on the mass scale for retired A stars.

astro-ph.SR↗

arXiv2017

Robo-AO Kepler Asteroseismic Survey. I. Adaptive optics imaging of 99 asteroseismic Kepler dwarfs and subgiants

We used the Robo-AO laser adaptive optics system to image 99 main sequence and subgiant stars that have Kepler-detected asteroseismic signals. Robo-AO allows us to resolve blended secondary sources at separations as close as 0.15" that may contribute to the measured Kepler light curves and affect asteroseismic analysis and interpretation. We report 8 new secondary sources within 4.0" of these Kepler asteroseismic stars. We used Subaru and Keck adaptive optics to measure differential infrared photometry for these candidate companion systems. Two of the secondary sources are likely foreground objects and at least 6 of the secondaries are background sources; however we cannot exclude the possibility that three of the objects may be physically associated. We measured a range of i'-band amplitude dilutions for the candidate companion systems from 0.43% to 15.4%. We find that the measured amplitude dilutions are insufficient to explain the previously identified excess scatter in the relationship between asteroseismic oscillation amplitude and the frequency of maximum power.

astro-ph.SR↗

arXiv2017

Evidence for spatially-correlated ${\it Gaia}$ parallax errors in the ${\it Kepler}$ field

We present evidence for a spatially-dependent systematic error in the first data release of ${\it Gaia}$ parallaxes based on comparisons to asteroseismic parallaxes in the ${\it Kepler}$ field, and present a parametrized model of the angular dependence of these systematics. We report an error of $0.059^{+0.004}_{-0.004}$mas on scales of 0.3deg, which decreases for larger scales to become $0.011^{+0.006}_{-0.004}$mas at 8deg. This is consistent with the $\sim2\%$ zeropoint offset for the whole sample discussed by Huber et al., and is compatible with the effect predicted by the ${\it Gaia}$ team. Our results are robust to dust prescriptions and choices in temperature scales used to calculate asteroseismic parallaxes. We also do not find evidence for significant differences in the signal when using red clump versus red giant stars. Our approach allows us to quantify and map the correlations in an astrophysically interesting field, resulting in a parametrized model of the spatial systematics that can be used to construct a covariance matrix for any work that relies upon TGAS parallaxes.

astro-ph.SR↗

arXiv2017

The more the merrier: grid based modelling of Kepler dwarfs with 5-dimensional stellar grids

We present preliminary results of our grid based modelling (GBM) of the dwarf/subgiant sample of stars observed with Kepler including global asteroseismic parameters. GBM analysis in this work is based on a large grid of stellar models that is characterized by five independent parameters: model mass and age, initial metallicity ($\zini$), initial helium ($\yini$), and mixing length parameter ($α_{mlt}$). Using this grid relaxes assumptions used in all previous GBM work where the initial composition is determined by a single parameter and that $α_{mlt}$ is fixed to a solar-calibrated value. The new grid allows us to study, for example, the impact of different galactic chemical enrichment models on the determination of stellar parameters such as mass radius and age. Also, it allows to include new results from stellar atmosphere models on $α_{mlt}$ in the GBM analysis in a simple manner. Alternatively, it can be tested if global asteroseismology is a useful tool to constraint our ignorance on quantities such as $\yini$ and $α_{mlt}$. Initial findings show that mass determination is robust with respect to freedom in the latter quantities, with a 4.4\% maximum deviation for extreme assumptions regarding prior information on $\yini-\zini$ relations and $α_{mlt}$. On the other hand, tests carried out so far seem to indicate that global seismology does not have much power to constrain $\yini-\zini$ relations of $α_{mlt}$ values without resourcing to additional information.

astro-ph.SR↗

arXiv2017

Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes

We present a comparison of parallaxes and radii from asteroseismology and Gaia DR1 (TGAS) for 2200 Kepler stars spanning from the main sequence to the red giant branch. We show that previously identified offsets between TGAS parallaxes and distances derived from asteroseismology and eclipsing binaries have likely been overestimated for parallaxes <~ 5-10 mas (~ 90-98% of the TGAS sample). The observed differences in our sample can furthermore be partially compensated by adopting a hotter Teff scale (such as the infrared flux method) instead of spectroscopic temperatures for dwarfs and subgiants. Residual systematic differences are at the ~ 2% level in parallax across three orders of magnitude. We use TGAS parallaxes to empirically demonstrate that asteroseismic radii are accurate to ~ 5% or better for stars between ~ 0.8-8 Rsun. We find no significant offset for main-sequence (<~ 1.5 Rsun) and low-luminosity RGB stars (~ 3-8 Rsun), but seismic radii appear to be systematically underestimated by ~5% for subgiants (~ 1.5-3 Rsun). We find no systematic errors as a function of metallicity between [Fe/H] ~ -0.8 to +0.4 dex, and show tentative evidence that corrections to the scaling relation for the large frequency separation (Dnu) improve the agreement with TGAS for RGB stars. Finally, we demonstrate that beyond ~ 3 kpc asteroseismology will provide more precise distances than end-of-mission Gaia data, highlighting the synergy and complementary nature of Gaia and asteroseismology for studying galactic stellar populations.

astro-ph.SR↗

arXiv2017

Evidence for compact binary systems around Kepler red giants

We present an analysis of 168 oscillating red giants from NASA's $Kepler$ mission that exhibit anomalous peaks in their Fourier amplitude spectra. These peaks result from ellipsoidal variations which are indicative of binary star systems, at frequencies such that the orbit of any stellar companion would be within the convective envelope of the red giant. Alternatively, the observed phenomenon may be due to a close binary orbiting a red giant in a triple system, or chance alignments of foreground or background binary systems contaminating the target pixel aperture. We identify 87 stars in the sample as chance alignments using a combination of pixel Fourier analysis and difference imaging. We find that in the remaining 81 cases the anomalous peaks are indistinguishable from the target star to within 4$''$, suggesting a physical association. We examine a Galaxia model of the $Kepler$ field of view to estimate background star counts and find that it is highly unlikely that all targets can be explained by chance alignments. From this, we conclude that these stars may comprise a population of physically associated systems.

astro-ph.SR↗

arXiv2017

Kepler-1649b: An Exo-Venus in the Solar Neighborhood

The Kepler mission has revealed that Earth-sized planets are common, and dozens have been discovered to orbit in or near their host star's habitable zone. A major focus in astronomy is to determine which of these exoplanets are likely to have Earth-like properties that are amenable to follow-up with both ground- and future space-based surveys, with an ultimate goal of probing their atmospheres to look for signs of life. Venus-like atmospheres will be of particular interest in these surveys. While Earth and Venus evolved to have similar sizes and densities, it remains unclear what factors led to the dramatic divergence of their atmospheres. Studying analogs to both Earth and Venus can thus shed light on the limits of habitability and the potential for life on known exoplanets. Here we present the discovery and confirmation of Kepler-1649b, an Earth-sized planet orbiting a nearby M5V star that receives incident flux at a level similar to that of Venus. We present our methods for characterizing the star, using a combination of PSF photometry, ground-based spectroscopy and imaging, to confirm the planetary nature of Kepler-1649b. Planets like Kepler-1649b will be prime candidates for atmospheric and habitability studies in the next generation of space missions.

astro-ph.EP↗

arXiv2017

Weighing in on the masses of retired A stars with asteroseismology: K2 observations of the exoplanet-host star HD 212771

Doppler-based planet surveys point to an increasing occurrence rate of giant planets with stellar mass. Such surveys rely on evolved stars for a sample of intermediate-mass stars (so-called retired A stars), which are more amenable to Doppler observations than their main-sequence progenitors. However, it has been hypothesised that the masses of subgiant and low-luminosity red-giant stars targeted by these surveys --- typically derived from a combination of spectroscopy and isochrone fitting --- may be systematically overestimated. Here, we test this hypothesis for the particular case of the exoplanet-host star HD 212771 using K2 asteroseismology. The benchmark asteroseismic mass ($1.45^{+0.10}_{-0.09}\:\text{M}_{\odot}$) is significantly higher than the value reported in the discovery paper ($1.15\pm0.08\:\text{M}_{\odot}$), which has been used to inform the stellar mass-planet occurrence relation. This result, therefore, does not lend support to the above hypothesis. Implications for the fates of planetary systems are sensitively dependent on stellar mass. Based on the derived asteroseismic mass, we predict the post-main-sequence evolution of the Jovian planet orbiting HD 212771 under the effects of tidal forces and stellar mass loss.

astro-ph.SR↗

arXiv2017

The Correlation Between Mixing Length and Metallicity on the Giant Branch: Implications for Ages in the Gaia Era

In the updated APOGEE-Kepler catalog, we have asteroseismic and spectroscopic data for over 3000 first ascent red giants. Given the size and accuracy of this sample, these data offer an unprecedented test of the accuracy of stellar models on the post-main-sequence. When we compare these data to theoretical predictions, we find a metallicity dependent temperature offset with a slope of around 100 K per dex in metallicity. We find that this effect is present in all model grids tested and that theoretical uncertainties in the models, correlated spectroscopic errors, and shifts in the asteroseismic mass scale are insufficient to explain this effect. Stellar models can be brought into agreement with the data if a metallicity dependent convective mixing length is used, with $ Δα_{\rm ML, YREC} \sim 0.2$ per dex in metallicity, a trend inconsistent with the predictions of three dimensional stellar convection simulations. If this effect is not taken into account, isochrone ages for red giants from the Gaia data will be off by as much as a factor of 2 even at modest deviations from solar metallicity ([Fe/H]=$-$0.5).

astro-ph.SR↗

arXiv2017

Revised Stellar Properties of Kepler Targets for the Q1-17 (DR25) Transit Detection Run

The determination of exoplanet properties and occurrence rates using Kepler data critically depends on our knowledge of the fundamental properties (such as temperature, radius and mass) of the observed stars. We present revised stellar properties for 197,096 Kepler targets observed between Quarters 1-17 (Q1-17), which were used for the final transiting planet search run by the Kepler Mission (Data Release 25, DR25). Similar to the Q1--16 catalog by Huber et al. the classifications are based on conditioning published atmospheric parameters on a grid of Dartmouth isochrones, with significant improvements in the adopted methodology and over 29,000 new sources for temperatures, surface gravities or metallicities. In addition to fundamental stellar properties the new catalog also includes distances and extinctions, and we provide posterior samples for each stellar parameter of each star. Typical uncertainties are ~27% in radius, ~17% in mass, and ~51% in density, which is somewhat smaller than previous catalogs due to the larger number of improved logg constraints and the inclusion of isochrone weighting when deriving stellar posterior distributions. On average, the catalog includes a significantly larger number of evolved solar-type stars, with an increase of 43.5% in the number of subgiants. We discuss the overall changes of radii and masses of Kepler targets as a function of spectral type, with particular focus on exoplanet host stars.

astro-ph.SR↗

arXiv2017

Phonon-assisted two-photon interference from remote quantum emitters

Photonic quantum technologies are on the verge of finding applications in everyday life with quantum cryptography and the quantum internet on the horizon. Extensive research has been carried out to determine suitable quantum emitters and single epitaxial quantum dots are emerging as near-optimal sources of bright, on-demand, highly indistinguishable single photons and entangled photon pairs. In order to build up quantum networks, it is now essential to interface remote quantum emitters. However, this is still an outstanding challenge, as the quantum states of dissimilar 'artificial atoms' have to be prepared on-demand with high fidelity, and the generated photons have to be made indistinguishable in all possible degrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51+/-5%) from remote strain-tunable GaAs quantum dots, emitting on-demand photon-pairs. We achieve this result by exploiting for the first time the full potential of the novel phonon-assisted two-photon excitation scheme, which allows for the generation of highly indistinguishable (visibility of 71+/-9%) entangled photon-pairs (fidelity of 90+/-2%), it enables push-to button biexciton state preparation (fidelity of 80+/-2%) and it outperforms conventional resonant two-photon excitation schemes in terms of robustness against environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeaters and complex multi-photon entanglement experiments involving dissimilar artificial atoms.

cond-mat.mes-hall↗

arXiv2017

Guaranteed Parameter Estimation for Discrete Energy Minimization

Structural learning, a method to estimate the parameters for discrete energy minimization, has been proven to be effective in solving computer vision problems, especially in 3D scene parsing. As the complexity of the models increases, structural learning algorithms turn to approximate inference to retain tractability. Unfortunately, such methods often fail because the approximation can be arbitrarily poor. In this work, we propose a method to overcome this limitation through exploiting the properties of the joint problem of training time inference and learning. With the help of the learning framework, we transform the inapproximable inference problem into a polynomial time solvable one, thereby enabling tractable exact inference while still allowing an arbitrary graph structure and full potential interactions. Our learning algorithm is guaranteed to return a solution with a bounded error to the global optimal within the feasible parameter space. We demonstrate the effectiveness of this method on two point cloud scene parsing datasets. Our approach runs much faster and solves a problem that is intractable for previous, well-known approaches.

cs.CV↗

arXiv2017

Stellar population synthesis based modelling of the Milky Way using asteroseismology of dwarfs and subgiants from Kepler

Early attempts to apply asteroseismology to study the Galaxy have already shown unexpected discrepancies for the mass distribution of stars between the Galactic models and the data; a result that is still unexplained. Here, we revisit the analysis of the asteroseismic sample of dwarf and subgiant stars observed by Kepler and investigate in detail the possible causes for the reported discrepancy. We investigate two models of the Milky Way based on stellar population synthesis, Galaxia and TRILEGAL. In agreement with previous results, we find that TRILEGAL predicts more massive stars compared to Galaxia, and that TRILEGAL predicts too many blue stars compared to 2MASS observations. Both models fail to match the distribution of the stellar sample in $(\log g,T_{\rm eff})$ space, pointing to inaccuracies in the models and/or the assumed selection function. When corrected for this mismatch in $(\log g,T_{\rm eff})$ space, the mass distribution calculated by Galaxia is broader and the mean is shifted toward lower masses compared to that of the observed stars. This behaviour is similar to what has been reported for the Kepler red giant sample. The shift between the mass distributions is equivalent to a change of 2\% in $ν_{\rm max}$, which is within the current uncertainty in the $ν_{\rm max}$ scaling relation. Applying corrections to the $Δν$ scaling relation predicted by the stellar models makes the observed mass distribution significantly narrower, but there is no change to the mean.

astro-ph.GA↗

arXiv2016

Electrically-Pumped Wavelength-Tunable GaAs Quantum Dots Interfaced with Rubidium Atoms

We demonstrate the first wavelength-tunable electrically-pumped source of non-classical light that can emit photons with wavelength in resonance with the D2 transitions of 87Rb atoms. The device is fabricated by integrating a novel GaAs single-quantum-dot light-emitting-diode (LED) onto a piezoelectric actuator. By feeding the emitted photons into a 75-mm-long cell containing warm 87Rb atom vapor, we observe slow-light with a temporal delay of up to 3.4 ns. In view of the possibility of using 87Rb atomic vapors as quantum memories, this work makes an important step towards the realization of hybrid-quantum systems for future quantum networks.

cond-mat.mes-hall↗

arXiv2016

Standing on the shoulders of Dwarfs: the Kepler asteroseismic LEGACY sample II - radii, masses, and ages

We use asteroseismic data from the Kepler satellite to determine fundamental stellar properties of the 66 main-sequence targets observed for at least one full year by the mission. We distributed tens of individual oscillation frequencies extracted from the time series of each star among seven modelling teams who applied different methods to determine radii, masses, and ages for all stars in the sample. Comparisons among the different results reveal a good level of agreement in all stellar properties, which is remarkable considering the variety of codes, input physics and analysis methods employed by the different teams. Average uncertainties are of the order of $\sim$2\% in radius, $\sim$4\% in mass, and $\sim$10\% in age, making this the best-characterised sample of main-sequence stars available to date. Our predicted initial abundances and mixing-length parameters are checked against inferences from chemical enrichment laws $ΔY / ΔZ$ and predictions from 3D atmospheric simulations. We test the accuracy of the determined stellar properties by comparing them to the Sun, angular diameter measurements, Gaia parallaxes, and binary evolution, finding excellent agreement in all cases and further confirming the robustness of asteroseismically-determined physical parameters of stars when individual frequencies of oscillation are available. Baptised as the Kepler dwarfs LEGACY sample, these stars are the solar-like oscillators with the best asteroseismic properties available for at least another decade. All data used in this analysis and the resulting stellar parameters are made publicly available for the community.

astro-ph.SR↗