18 research outputs found
Orbital Elements and Stellar Parameters of the Active Binary UX Arietis
This is the final version of the article. Available from American Astronomical Society via the DOI in this record.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 WilsonâDevinney 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 (MP = 1.30 0.06 M, MS = 1.14 0.06 M). The radius of the primary can be determined to be
RP = 5.6 0.1 R and that of the secondary to be RS = 1.6 0.2 R. The equivalent spot coverage of the
primary component was found to be 62% with an effective temperature 20% below that of the unspotted surface.We thank Robert Wilson (University of Florida) for providing a custom version of his code to compute images of spotted stellar surfaces and for his help with using it. This work is based upon observations obtained with the Georgia State University (GSU) Center for High Angular Resolution Astronomy (CHARA) array at Mount Wilson Observatory. The CHARA array is supported by the National Science Foundation under grant numbers AST-1211929 and AST-1411654. Institutional support has been provided by the GSU College of Arts and Sciences and the GSU Office of the Vice President for Research and Economic Development. The MIRC instrument at the CHARA array was funded by the University of Michigan. F.B., R.R., and J.D.M. acknowledge support from NSF-AST 1210972 and 1108963. G.T. acknowledges partial support from NSF grant AST-1509375. S.K. acknowledges support from an STFC Rutherford Fellowship (ST/J004030/1) and ERC Starting Grant (grant agreement no. 639889). This work is also based on observations made with the Nordic Optical Telescope (NOT), operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. This research has made use of the SIMBAD database, operated at the CDS, Strasbourg, France. This research has made use of the Jean-Marie Mariotti Center SearchCal service13 codeveloped by FIZEAU and LAOG/IPAG and of the CDS astronomical databases SIMBAD and VIZIER.14 This research has made use of the Washington Double Star Catalog, maintained at the U.S. Naval Observatory. We thank Nicholas Elias II for discussions. We thank Dimitri Pourbaix for maintaining and providing access to the SB9 database of RV measurements of spectroscopic binaries
Contemporaneous Imaging Comparisons of the Spotted Giant Ï Geminorum Using Interferometric, Spectroscopic, and Photometric Data
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
Precision Orbit of ÎŽ Delphini and Prospects for Astrometric Detection of Exoplanets
This is the author accepted manuscript. The final version is available from American Astronomical Society / IOP Publishing via the DOI in this record.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 ÎŽ 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 ÎŽ Del, along with masses of 1.78 ± 0.07 M â and 1.62 ± 0.07 M â 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 ~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 2 M J on orbits >0.75 au around individual components of hot binary stars via differential astrometry.This work is based upon observations obtained with the Georgia State University Center for High Angular Resolution
Astronomy Array at Mount Wilson Observatory. The CHARA Array is supported by the National Science Foundation
under Grants No. AST-1211929 and AST-1411654. Institutional support has been provided from the GSU College of
Arts and Sciences and the GSU Office of the Vice President for Research and Economic Development. This research
has made use of the Jean-Marie Mariotti Center SearchCal service2
. JDM and TG wish to gratefully acknowledge
support by NASA XRP Grant NNX16AD43G. Astronomy at Tennessee State University is supported by the state of
Tennessee through its Centers of Excellence program. SK acknowledges support from an European Research Council
Starting Grant (Grant Agreement No. 639889) and STFC Rutherford Fellowship (ST/J004030/1). D.H. acknowledges
support by the National Aeronautics and Space Administration under Grant NNX14AB92G issued through the Kepler
Participating Scientist Program. TRW acknowledges the support of the Villum Foundation (research grant 10118)
A geometrical 1% distance to the short-period binary Cepheid V1334 Cygni
This is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this record.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 PeriodâLuminosity (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 d period Cepheid V1334 Cyg with
an unprecedented accuracy of ±1 %, providing the most accurate distance for a Cepheid. Placing this
star in the PâL diagram provides an independent test of existing period-luminosity 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 PâL 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 PâL 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, M1 = 4.288±0.133 M (Cepheid) and M2 = 4.040±0.048 M
(companion), providing the most accurate masses for a Galactic binary Cepheid systemThis research is based on observations made with
SOPHIE spectrograph on the 1.93-m telescope at Ob-
A geometrical 1 % distance to a short-period binary Cepheid 11
servatoire de Haute-Provence (CNRS/AMU), France
(ProgID: 13A.PNPS10, 13B.PNPS003, 14A.PNPS010,
15A.PNPS010, 16B.PNPS.KERV). This research is
based on observations made with the Mercator Telescope,
operated on the island of La Palma by the Flemish
Community, at the Spanish Observatorio del Roque
de los Muchachos of the Instituto de Astrofsica de Canarias.
Hermes is supported by the Fund for Scientific
Research of Flanders (FWO), Belgium; the Research
Council of K.U.Leuven, Belgium; the Fonds National
de la Recherche Scientifique (F.R.S.- FNRS), Belgium;
the Royal Observatory of Belgium; the Observatoire de
Genve, Switzerland; and the Thšuringer Landessternwarte,
Tautenburg, Germany. This work is also based
on observations with the NASA/ESA Hubble Space
Telescope obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA
contract NAS5-26555 (ProgID 13454). We acknowledge
the support of the French Agence Nationale de
la Recherche (ANR-15-CE31-0012-01, project UnlockCepheids).
WG and GP gratefully acknowledge financial
support from the BASAL Centro de Astrofisica
y Tecnologias Afines (CATA, AFB-170002). WG also
acknowledges financial support from the Millenium Institute
of Astrophysics (MAS) of the Iniciativa Cientifica
Milenio del Ministerio de Economia, Fomento y
Turismo de Chile (project IC120009). We acknowledge
financial support from the Programme National
de Physique Stellaire (PNPS) of CNRS/INSU, France.
Support from the Polish National Science Centre grants
MAESTRO UMO-2017/26/A/ST9/00446 and from the
IdP II 2015 0002 64 grant of the Polish Ministry of
Science and Higher Education is also acknowledged.
The research leading to these results has received funding
from the European Research Council (ERC) under
the European Unionâs Horizon 2020 research and innovation
programme (grant agreement No. 695099 and
639889). NRE acknowledge support from the Chandra
X-ray Center NASA (contract NAS8-03060) and
the HST grants GO-13454.001-A and GO-14194.002.
This work is based upon observations obtained with
the Georgia State University Center for High Angular
Resolution Astronomy Array at Mount Wilson Observatory.
The CHARA Array is supported by the National
Science Foundation under Grants No. AST-1211929,
1411654, and 1636624. Institutional support has been
provided from the GSU College of Arts and Sciences
and the GSU Office of the Vice President for Research
and Economic Development. BP acknowledges financial
support from the Polish National Science Center grant
SONATA 2014/15/D/ST9/02248
The Expanding Fireball of Nova Delphini 2013
A classical nova occurs when material accreting onto the surface of a white
dwarf in a close binary system ignites in a thermonuclear runaway. Complex
structures observed in the ejecta at late stages could result from interactions
with the companion during the common envelope phase. Alternatively, the
explosion could be intrinsically bipolar, resulting from a localized ignition
on the surface of the white dwarf or as a consequence of rotational distortion.
Studying the structure of novae during the earliest phases is challenging
because of the high spatial resolution needed to measure their small sizes.
Here we report near-infrared interferometric measurements of the angular size
of Nova Delphini 2013, starting from one day after the explosion and continuing
with extensive time coverage during the first 43 days. Changes in the apparent
expansion rate can be explained by an explosion model consisting of an
optically thick core surrounded by a diffuse envelope. The optical depth of the
ejected material changes as it expands. We detect an ellipticity in the light
distribution, suggesting a prolate or bipolar structure that develops as early
as the second day. Combining the angular expansion rate with radial velocity
measurements, we derive a geometric distance to the nova of 4.54 +/- 0.59 kpc
from the Sun.Comment: Published in Nature. 32 pages. Final version available at
http://www.nature.com/nature/journal/v515/n7526/full/nature13834.htm
No Sun-like dynamo on the active star ζ Andromedae from starspot asymmetry
This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record.Sunspots are cool areas caused by strong surface magnetic fields inhibiting convection. Moreover, strong magnetic fields can alter the average atmospheric structure , degrading our ability to measure stellar masses and ages. Stars more active than the Sun have more and stronger dark spots than in the solar case, including on the rotational pole itself. Doppler imaging, which has so far produced the most detailed images of surface structures on other stars than the Sun, cannot always distinguish the hemisphere in which the starspots are located, especially in the equatorial region and if the data quality is not optimal . This leads to problems in investigating the north-south distribution of starspot active latitudes (those latitudes with more spot activity), which are crucial constraints of dynamo theory. Polar spots, inferred only from Doppler tomography, could plausibly be observational artifacts, casting some doubt on their very existence. Here we report imaging of the old, magnetically-active star ζ Andromedae using long-baseline infrared interferometry. In our data, a dark polar spot is seen in each of two epochs, while lower-latitude spot structures in both hemispheres do not persist between observations revealing global starspot asymmetries. The north-south symmetry of active latitudes observed on the Sun is absent on ζ And, which hosts global spot patterns that cannot be produced by solar-type dynamos.National Science Foundation (NSF)Hungarian Academy of Science
EXPRES. III. Revealing the stellar activity radial velocity signature of Ï” Eridani with photometry and interferometry
This is the final version. Available from IOP Publishing via the DOI in this record.âŻThe distortions of absorption line profiles caused by photospheric brightness variations on the surfaces of cool, main-sequence stars can mimic or overwhelm radial velocity (RV) shifts due to the presence of exoplanets. The latest generation of precision RV spectrographs aims to detect velocity amplitudes âČ 10 cm s-1, but requires mitigation of stellar signals. Statistical techniques are being developed to differentiate between Keplerian and activity-related velocity perturbations. Two important challenges, however, are the interpretability of the stellar activity component as RV models become more sophisticated, and ensuring the lowest-amplitude Keplerian signatures are not inadvertently accounted for in flexible models of stellar activity. For the K2V exoplanet host Eridani, we separately used ground-based photometry to constrain Gaussian processes for modeling RVs and TESS photometry with a light-curve inversion algorithm to reconstruct the stellar surface. From the reconstructions of TESS photometry, we produced an activity model that reduced the rms scatter in RVs obtained with EXPRES from 4.72 to 1.98 m s-1. We present a pilot study using the CHARA Array and MIRC-X beam combiner to directly image the starspots seen in the TESS photometry. With the limited phase coverage, our spot detections are marginal with current data but a future dedicated observing campaign should allow for imaging, as well as allow the stellar inclination and orientation with respect to the debris disk to be definitively determined. This work shows that stellar surface maps obtained with high-cadence, time-series photometric and interferometric data can provide the constraints needed to accurately reduce RV scatter.European CommissionNSFNSFNASANASA XRPEuropean Research CouncilNASA TESS GIHeising-Simons FoundationAnonymous donor in the Yale alumni communityYale Center for Astronomy and Astrophysics Prize Postdoctoral FellowshipHeising-Simons 51 Pegasi b Postdoctoral Fellowshi
Establishing α Oph as a Prototype Rotator: Precision Orbit with new Keck, CHARA, and RV Observations
This is the author accepted manuscript. The final version is available from the American Astronomical Society via the DOI in this recordAlpha Ophiuchi (Rasalhague) is a nearby rapidly rotating A5IV star which has been imaged by infrared interferometry. α Oph is also part of a known binary system, with a companion semi-major axis of âŒ430 milli-arcseconds and high eccentricity of 0.92. The binary companion provides the unique opportunity to measure the dynamical mass to compare with the results of rapid rotator evolution models. The lack of data near periastron passage limited the precision of mass measurements in previous work. We add new interferometric data from the MIRC combiner at the CHARA Array as well as new Keck adaptive optics imaging data with NIRC2, including epochs taken near periastron passage. We also obtained new radial velocities of both components at Fairborn Observatory. Our updated combined orbit for the system drastically reduces the errors of the orbital elements, and allows for precise measurement of the primary star mass at the few percent level. Our resulting primary star mass of 2.20±0.06 Mâ agrees well with predictions from imaging results, and matches evolution models with rotation when plotting on an HR diagram. However, to truly distinguish between non-rotating and rotating evolution models for this system we need âŒ1\% errors on mass, which might be achieved once the distance is known to higher precision in future Gaia releases. We find that the secondary mass of 0.824±0.023 Mâ is slightly under-luminous when compared to stellar evolution models. We show that α Oph is a useful reference source for programs that need ±1 milli-arcsecond astrometry.NASANational Science Foundation (NSF)European Research Council (ERC