| 1. |
- De Rosa, G., et al.
(författare)
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Velocity-resolved Reverberation Mapping of Five Bright Seyfert 1 Galaxies
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 866:2
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Gallenne, A., et al.
(författare)
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A Geometrical 1% Distance to the Short-period Binary Cepheid V1334 Cygni
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 867:2
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Gardner, Tyler, et al.
(författare)
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Precision Orbit of delta Delphini and Prospects for Astrometric Detection of Exoplanets
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 855:1, s. 1-18
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Hoard, D. W., et al.
(författare)
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Multiwavelength Ground and Space Observations of the Variable White Dwarf BOKS 53856 : Nonuniform Metal Absorption in Dark Spots
- 2018
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 156:3
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Tidskriftsartikel (refereegranskat)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.
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| 5. |
- Hummel, C. A., et al.
(författare)
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Orbital Elements and Stellar Parameters of the Active Binary UX Arietis
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 844:2
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Tidskriftsartikel (refereegranskat)abstract
- Stellar activity observed as large surface spots, radio flares, or emission lines is often found in binary systems. UX Arietis exhibits these signs of activity, originating on the K0 subgiant primary component. Our aim is to resolve the binary, measure the orbital motion, and provide accurate stellar parameters such as masses and luminosities to aid in the interpretation of the observed phenomena. Using the CHARA six-telescope optical long-baseline array on Mount Wilson, California, we obtained amplitudes and phases of the interferometric visibility on baselines up to 330 m in length, resolving the two components of the binary. We reanalyzed archival Center for Astrophysics spectra to disentangle the binary component spectra and the spectrum of the third component, which was resolved by speckle interferometry. We also obtained new spectra with the Nordic Optical Telescope, and we present new photometric data that we use to model stellar surface spot locations. Both interferometric visibilities and spectroscopic radial velocities are modeled with a spotted primary stellar surface using the Wilson-Devinney code. We fit the orbital elements to the apparent orbit and radial velocity data to derive the distance (52.1 +/- 0.8 pc) and stellar masses (M-P = 1.30 +/- 0.06 M-circle dot, M-S = 1.14 +/- 0.06 M-circle dot). The radius of the primary can be determined to be R-P = 5.6 +/- 0.1 R-circle dot and that of the secondary to be R-S = 1.6 +/- 0.2 R-circle dot. The equivalent spot coverage of the primary component was found to be 62% with an effective temperature 20% below that of the unspotted surface.
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| 6. |
- Kochukhov, Oleg, et al.
(författare)
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Surface magnetism of cool stars
- 2017
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - : WILEY-V C H VERLAG GMBH. - 0004-6337 .- 1521-3994. ; 338:4, s. 428-441
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic fields are essential ingredients of many physical processes in the interiors and envelopes of cool stars. Yet their direct detection and characterization is notoriously difficult, requiring high-quality observations and advanced analysis techniques. Significant progress has been recently achieved by several types of direct magnetic field studies on the surfaces of cool, active stars. In particular, complementary techniques of field topology mapping with polarization data and total magnetic flux measurements from intensity spectra have been systematically applied to different classes of active stars, leading to interesting and occasionally controversial results. In this paper, we summarize the current status of direct magnetic field studies of cool stars and investigations of surface inhomogeneities caused by the field, based on the material presented at the Cool Stars 19 splinter session.
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| 7. |
- Roettenbacher, Rachael M., et al.
(författare)
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Contemporaneous Imaging Comparisons of the Spotted Giant sigma Geminorum Using Interferometric, Spectroscopic, and Photometric Data
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 849:2
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Tidskriftsartikel (refereegranskat)abstract
- Nearby active stars with relatively rapid rotation and large starspot structures offer the opportunity to compare interferometric, spectroscopic, and photometric imaging techniques. In this paper, we image a spotted star with three different methods for the first time. The giant primary star of the RS Canum Venaticorum binary sigma. Geminorum (sigma Gem) was imaged for two epochs of interferometric, high-resolution spectroscopic, and photometric observations. The light curves from the reconstructions show good agreement with the observed light curves, supported by the longitudinally consistent spot features on the different maps. However, there is strong disagreement in the spot latitudes across the methods.
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| 8. |
- Roettenbacher, Rachael M., et al.
(författare)
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KOI-1003 : A NEW SPOTTED, ECLIPSING RS CVN BINARY IN THE KEPLER FIELD
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 832:2
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Tidskriftsartikel (refereegranskat)abstract
- Using the high-precision photometry from the Kepler space telescope, thousands of stars with stellar and planetary companions have been observed. The characterization of stars with companions is not always straightforward and can be contaminated by systematic and stellar influences on the light curves. Here, through a detailed analysis of starspots and eclipses, we identify KOI-1003 as a new, active RS CVn star-the first identified with data from Kepler. The Kepler light curve of this close binary system exhibits the system's primary transit, secondary eclipse, and starspot evolution of two persistent active longitudes. The near equality of the system's orbital and rotation periods indicates the orbit and primary star's rotation are nearly synchronized (P-orb = 8.360613 +/- 0.000003 days; P-rot similar to 8.23 days). By assuming the secondary star is on the main sequence, we suggest the system consists of a 1.45(-0.19)(+0.11) M-circle dot subgiant primary and a 0.59(-0.04)(+0.03) M-circle dot main-sequence companion. Our work gives a distance of 4400 +/- 600 pc and an age of t = 3.0(+2.0)(-0.5) Gyr, parameters which are discrepant with previous studies that included the star as a member of the open cluster NGC 6791.
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| 9. |
- Roettenbacher, Rachael M., et al.
(författare)
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The Connection between Starspots and Flares on Main-sequence Kepler Stars
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 868:1
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Tidskriftsartikel (refereegranskat)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.
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| 10. |
- Roettenbacher, Rachael M., et al.
(författare)
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The Stellar Activity of TRAPPIST-1 and Consequences for the Planetary Atmospheres
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 851:2
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Tidskriftsartikel (refereegranskat)abstract
- The signatures of planets hosted by M dwarfs are more readily detected with transit photometry and radial velocity methods than those of planets around larger stars. Recently, transit photometry was used to discover seven planets orbiting the late-M dwarf TRAPPIST-1. Three of TRAPPIST-1's planets fall in the Habitable Zone, a region where liquid water could exist on the planetary surface given appropriate planetary conditions. We aim to investigate the habitability of the TRAPPIST-1 planets by studying the star's activity and its effect on the planets. We analyze previously published space-and ground-based light curves and show the photometrically determined rotation period of TRAPPIST-1 appears to vary over time due to complicated, evolving surface activity. The dramatic changes of the surface of TRAPPIST-1 suggest that rotation periods determined photometrically may not be reliable for this and similarly active stars. While the activity of the star is low, we use the premise of the cosmic shoreline to provide evidence that the TRAPPIST-1 environment has potentially led to the erosion of possible planetary atmospheres by extreme ultraviolet stellar emission.
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