| 1. |
- De Rosa, G., et al.
(author)
-
Velocity-resolved Reverberation Mapping of Five Bright Seyfert 1 Galaxies
- 2018
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 866:2
-
Journal article (peer-reviewed)abstract
- We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-H beta reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure H beta time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent H beta lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.
|
|
| 2. |
- Gallenne, A., et al.
(author)
-
A Geometrical 1% Distance to the Short-period Binary Cepheid V1334 Cygni
- 2018
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 867:2
-
Journal article (peer-reviewed)abstract
- Cepheid stars play a considerable role as extragalactic distances indicators, thanks to the simple empirical relation between their pulsation period and their luminosity. They overlap with that of secondary distance indicators, such as Type Ia supernovae, whose distance scale is tied to Cepheid luminosities. However, the period-luminosity (P-L) relation still lacks a calibration to better than 5%. Using an original combination of interferometric astrometry with optical and ultraviolet spectroscopy, we measured the geometrical distance d = 720.35 +/- 7.84 pc of the 3.33 day period Cepheid V1334 Cyg with an unprecedented accuracy of +/- 1%, providing the most accurate distance for a Cepheid. Placing this star in the P-L diagram provides an independent test of existing P-L relations. We show that the secondary star has a significant impact on the integrated magnitude, particularly at visible wavelengths. Binarity in future high-precision calibrations of the P-L relations is not negligible, at least in the short-period regime. Subtracting the companion flux leaves V1334 Cyg in marginal agreement with existing photometric-based P-L relations, indicating either an overall calibration bias or a significant intrinsic dispersion at a few percent level. Our work also enabled us to determine the dynamical masses of both components, M-1 = 4.288 +/- 0.133 M-circle dot (Cepheid) and M-2 = 4.040 +/- 0.048 M-circle dot (companion), providing the most accurate masses for a Galactic binary Cepheid system.
|
|
| 3. |
- Gardner, Tyler, et al.
(author)
-
Precision Orbit of delta Delphini and Prospects for Astrometric Detection of Exoplanets
- 2018
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 855:1, s. 1-18
-
Journal article (peer-reviewed)abstract
- Combining visual and spectroscopic orbits of binary stars leads to a determination of the full 3D orbit, individual masses, and distance to the system. We present a full analysis of the evolved binary system delta Delphini using astrometric data from the MIRC and PAVO instruments on the CHARA long-baseline interferometer, 97 new spectra from the Fairborn Observatory, and 87 unpublished spectra from the Lick Observatory. We determine the full set of orbital elements for delta Del, along with masses of 1.78 +/- 0.07 M-circle dot and 1.62 +/- 0.07 M-circle dot for each component, and a distance of 63.61 +/- 0.89 pc. These results are important in two contexts: for testing stellar evolution models and for defining the detection capabilities for future planet searches. We find that the evolutionary state of this system is puzzling, as our measured flux ratios, radii, and masses imply a similar to 200 Myr age difference between the components, using standard stellar evolution models. Possible explanations for this age discrepancy include mass transfer scenarios with a now-ejected tertiary companion. For individual measurements taken over a span of two years, we achieve <10 mu as precision on the differential position with 10 minute observations. The high precision of our astrometric orbit suggests that exoplanet detection capabilities are within reach of MIRC at CHARA. We compute exoplanet detection limits around delta Del and conclude that, if this precision is extended to wider systems, we should be able to detect most exoplanets >2M(J) on orbits >0.75 au around individual components of hot binary stars via differential astrometry.
|
|
| 4. |
- Hoard, D. W., et al.
(author)
-
Multiwavelength Ground and Space Observations of the Variable White Dwarf BOKS 53856 : Nonuniform Metal Absorption in Dark Spots
- 2018
-
In: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 156:3
-
Journal article (peer-reviewed)abstract
- We analyze extensive ground- and space-based ultraviolet-infrared observations of the variable white dwarf BOKS 53856. Photometry and spectroscopy were obtained from the Hubble Space Telescope, Spitzer Space Telescope, Kepler and Swift satellites, Palomar Observatory, and Kitt Peak National Observatory. Time series data spanning the entire four-year Kepler mission are used to refine the photometric rotation period of the white dwarf to 0.2557292(9) days. The associated periodic variability, with full (minimum to maximum) amplitudes of approximate to 5% and approximate to 10% in the optical and ultraviolet, respectively, is consistent with the presence of several dark spots on the white dwarf surface. A fit to the observed ultraviolet-infrared spectral energy distribution of BOKS 53856 using a grid of non-LTE synthetic spectra gives best values of effective temperature, T-WD = 31,056(19) K, surface gravity, log g = 7.913(5), mass, M-WD = 0.603(2) M-circle dot, radius, R-WD = 0.0142(4) R-circle dot, reddening, Eb-v = 0.0533(1), and distance, d = 277(10) pc. The Hubble ultraviolet spectrum does not show a detectable signature of accreted metals, and the Spitzer infrared photometry does not reveal an excess attributable to a circumstellar dust disk. Nonetheless, the ground-based optical spectra show a very weak, variable Ca II K absorption line that is phased with the Kepler light curve, being strongest at minimum brightness. We discuss BOKS 53856 and similar objects in the context of a localized enhancement of absorption from metals in dark (possibly magnetic) spots on the white dwarf surface.
|
|
| 5. |
- Roettenbacher, Rachael M., et al.
(author)
-
The Connection between Starspots and Flares on Main-sequence Kepler Stars
- 2018
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 868:1
-
Journal article (peer-reviewed)abstract
- Starspots and flares are indicators of stellar magnetic activity and can both be studied in greater detail by utilizing the long-term, space-based archive of the Kepler satellite. Here, we aim to investigate a subset of the Kepler archive to reveal a connection between the starspots and the stellar flares, in order to provide insight into the overall stellar magnetic field. We use the flare-finding algorithm FLATW'RM in conjunction with a new suite of algorithms that aim to locate the local minima caused by starspot groups. We compare the phase difference between the time of maximum flux of a flare and the time of minimum stellar flux due to a starspot group. The strongest flares do not appear to be correlated to the largest starspot group present, but are also not uniformly distributed in phase with respect to the starspot group. The weaker flares, however, do show an increased occurrence close to the starspot groups.
|
|
| 6. |
- Schaefer, Gail H., et al.
(author)
-
Interferometry in the era of time-domain astronomy
- 2018
-
In: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 46:3, s. 421-431
-
Journal article (peer-reviewed)abstract
- The physical nature of time variable objects is often inferred from photometric light-curves and spectroscopic variations. Long-baseline optical interferometry has the power to resolve the spatial structure of time variable sources directly in order to measure their physical properties and test the physics of the underlying models. Recent interferometric studies of variable objects include measuring the angular expansion and spatial structure during the early stages of novae outbursts, studying the transits and tidal distortions of the components in eclipsing and interacting binaries, measuring the radial pulsations in Cepheid variables, monitoring changes in the circumstellar discs around rapidly rotating massive stars, and imaging starspots. Future applications include measuring the image size and centroid displacements in gravitational microlensing events, and imaging the transits of exoplanets. Ongoing and upcoming photometric surveys will dramatically increase the number of time-variable objects detected each year, providing many potential targets to observe interferometrically. For short-lived transient events, it is critical for interferometric arrays to have the flexibility to respond rapidly to targets of opportunity and optimize the selection of baselines and beam combiners to provide the necessary resolution and sensitivity to resolve the source as its brightness and size change. We discuss the science opportunities made possible by resolving variable sources using long baseline optical interferometry.
|
|
| 7. |
- Vida, Krisztián, et al.
(author)
-
Finding flares in Kepler data using machine-learning tools
- 2018
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
-
Journal article (peer-reviewed)abstract
- Context. Archives of long photometric surveys, such as the Kepler database, are a great basis for studying flares. However, identifying the flares is a complex task; it is easily done in the case of single-target observations by visual inspection, but is nearly impossible for several year-long time series for several thousand targets. Although automated methods for this task exist, several problems are difficult (or impossible) to overcome with traditional fitting and analysis approaches.Aims. We introduce a code for identifying and analyzing flares based on machine-learning methods, which are intrinsically adept at handling such data sets.Methods. We used the RANSAC (RANdom SAmple Consensus) algorithm to model light curves, as it yields robust fits even in the case of several outliers, such as flares. The light curves were divided into search windows, approximately on the order of the stellar rotation period. This search window was shifted over the data set, and a voting system was used to keep false positives to a minimum: only those flare candidate points were kept that were identified as a flare in several windows.Results. The code was tested on short-cadence K2 observations of TRAPPIST-1 and on long-cadence Kepler data of KIC 1722506. The detected flare events and flare energies are consistent with earlier results from manual inspections.
|
|
