19 research outputs found
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and PAVO instruments on the CHARA long-baseline interferometer, 97 new spectra from the Fairborn Observatory, and 87 unpublished spectra from the Lick Observatory.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)
An asymmetric shock wave in the 2006 outburst of the recurrent nova RS Ophiuchi
Nova outbursts take place in binary star systems comprising a white dwarf and
either a low-mass Sun-like star or, as in the case of the recurrent nova RS
Ophiuchi, a red giant. Although the cause of these outbursts is known to be
thermonuclear explosion of matter transferred from the companion onto the
surface of the white dwarf, models of the previous (1985) outburst of RS
Ophiuchi failed to adequately fit the X-ray evolution and there was controversy
over a single-epoch high-resolution radio image, which suggested that the
remnant was bipolar rather than spherical as modelled. Here we report the
detection of spatially resolved structure in RS Ophiuchi from two weeks after
its 12 February 2006 outburst. We track an expanding shock wave as it sweeps
through the red giant wind, producing a remnant similar to that of a type II
supernova but evolving over months rather than millennia. As in supernova
remnants, the radio emission is non-thermal (synchrotron emission), but
asymmetries and multiple emission components clearly demonstrate that contrary
to the assumptions of spherical symmetry in models of the 1985 explosion, the
ejection is jet-like, collimated by the central binary whose orientation on the
sky can be determined from these observations.Comment: 10 pages, 4 figures, accepted by Natur
ARMADA. I. Triple Companions Detected in B-type Binaries α Del and Μ Gem
This is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this recordGround-based optical long-baseline interferometry has the power to measure the orbits of close binary systems at âŒ10 ÎŒas precision. This precision makes it possible to detect "wobbles" in the binary motion due to the gravitational pull from additional short-period companions. We started the ARrangement for Micro-Arcsecond Differential Astrometry (ARMADA) survey with the Michigan Infra-Red Combiner (MIRC)/MIRC-X instrument at the Center for High Angular Resoloution Astronomy (CHARA) array for the purpose of detecting giant planets and stellar companions orbiting individual stars in binary systems. We describe our observations for the survey, and introduce the wavelength calibration scheme that delivers precision at the tens of microarcseconds level for <0.âł2 binaries. We test our instrument performance on a known triple system, Îș Peg, and show that our survey is delivering a factor of 10 better precision than previous similar surveys. We present astrometric detections of tertiary components to two B-type binaries: a 30 day companion to α Del, and a 50 day companion to Îœ Gem. We also collected radial velocity data for α Del with the Tennessee State University Automated Spectroscopic Telescope at Fairborn Observatory. We are able to measure the orbits and masses of all three components in these systems. We find that the previously published radial velocity orbit for the inner pair of Îœ Gem is not consistent with our visual orbit. The precision achieved for these orbits suggests that our ARMADA survey will be successful at discovering new compact triple systems to A/B-type binary systems, leading to better statistics of hierarchical system architectures and formation history.NASANational Science Foundation (NSF)Michigan Space Grant ConsortiumEuropean Research Council (ERC)Science and Technology Facilities Council (STFC
X-Ray Emitting Blast Wave from the Recurrent Nova RS Ophiuchi
Stellar explosions such as novae and supernovae produce most of the heavy
elements in the Universe. Although the onset of novae from runaway
thermonuclear fusion reactions on the surface of a white dwarf in a binary star
system is understood[1], the structure, dynamics, and mass of the ejecta are
not well known. In rare cases, the white dwarf is embedded in the wind nebula
of a red-giant companion; the explosion products plow through the nebula and
produce X-ray emission. Early this year, an eruption of the recurrent nova RS
Ophiuchi[2,3] provided the first opportunity to perform comprehensive X-ray
observations of such an event and diagnose conditions within the ejecta. Here
we show that the hard X-ray emission from RS Ophiuchi early in the eruption
emanates from behind a blast wave, or outward-moving shock wave, that expanded
freely for less than 2 days and then decelerated due to interaction with the
nebula. The X-rays faded rapidly, suggesting that the blast wave deviates from
the standard spherical shell structure[4-6]. The early onset of deceleration
indicates that the ejected shell had a low mass, the white dwarf has a high
mass[7], and that RS Ophiuchi is a progenitor of the type of supernova integral
to studies of the expansion of the universe.Comment: To appear in Nature; 7 pages, including 2 color figures; removed
incorrect statement of embargo polic
A thesis to probe unique exoplanet regimes with micro-arcsecond astrometry and precision closure phases at CHARA and VLTI
This is the final version. Available from SPIE via the DOI in this recordSPIE Astronomical Telescopes + Instrumentation 2022, 17 - 22 July 2022, Montreal, CanadaIn this thesis work, we exploit the unique capabilities of long baseline interferometry to fill two gaps in exoplanet parameter space: 1) the discovery of new planets around stars more massive than the Sun (Project ARMADA), and 2) the characterization of known planets that are extremely close to their host star (Project PRIME). Current detection methods struggle to find exoplanets around hot (A/B-type) stars. We are pushing the astrometric limits of ground-based optical interferometers to carry out a survey of sub-arcsecond A/B-type binary systems with ARMADA. We are achieving astrometric precision at the few tens of micro-arcsecond level in short observations at CHARA/MIRC-X and VLTI/GRAVITY. This incredible precision allows us to probe the au-regime for giant planets orbiting individual stars of the binary system. We present the status of our survey, including our newly implemented etalon wavelength calibration method at CHARA, detection of new stellar mass companions, and non-detection limits down to a few Jupiter masses in some cases. With Project PRIME, we show that ground-based optical interferometry can be used to measure the orbit-dependent spectra of close-in âhot Jupiterâ-type exoplanets with precision closure phases. Detecting the infrared spectra of such planets allows us to place useful constraints on atmosphere circulation models. We perform injection tests with MIRC-X and MYSTIC at CHARA for the hot Jupiter exoplanet Ups And b to show that we are reaching down to a contrast of 2e-4. The promise of both these methods demonstrate that optical interferometers are a valuable tool for probing unique regimes of exoplanet science.NASANational Science Foundation (NSF)European Research Council (ERC)Science and Technology Facilities Council (STFC)European Union Horizon 202
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
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
Optical polarimetry: Methods, Instruments and Calibration Techniques
In this chapter we present a brief summary of methods, instruments and
calibration techniques used in modern astronomical polarimetry in the optical
wavelengths. We describe the properties of various polarization devices and
detectors used for optical broadband, imaging and spectropolarimetry, and
discuss their advantages and disadvantages. The necessity of a proper
calibration of the raw polarization data is emphasized and methods of the
determination and subtraction of instrumental polarization are considered. We
also present a few examples of high-precision measurements of optical
polarization of black hole X-ray binaries and massive binary stars made with
our DiPol-2 polarimeter, which allowed us to constrain the sources of optical
emission in black hole X-ray binaries and measure orbital parameters of massive
stellar binaries.Comment: 33 pages, 14 figure; to be published in Astrophysics and Space
Science Library 460, Astronomical Polarisation from the Infrared to Gamma
Ray
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
ARMADA II: Further Detections of Inner Companions to Intermediate Mass Binaries with Micro-Arcsecond Astrometry at CHARA and VLTI
This is the author accepted manuscript.We started a survey with CHARA/MIRC-X and VLTI/GRAVITY to search for low mass
companions orbiting individual components of intermediate mass binary systems.
With the incredible precision of these instruments, we can detect astrometric
"wobbles" from companions down to a few tens of micro-arcseconds. This allows
us to detect any previously unseen triple systems in our list of binaries. We
present the orbits of 12 companions around early F to B-type binaries, 9 of
which are new detections and 3 of which are first astrometric detections of
known RV companions. The masses of these newly detected components range from
0.45-1.3 solar masses. Our orbits constrain these systems to a high astrometric
precision, with median residuals to the orbital fit of 20-50 micro-arcseconds
in most cases. For 7 of these systems we include newly obtained radial velocity
data, which help us to identify the system configuration and to solve for
masses of individual components in some cases. Although additional RV
measurements are needed to break degeneracy in the mutual inclination, we find
that the majority of these inner triples are not well-aligned with the wide
binary orbit. This hints that higher mass triples are more misaligned compared
to solar and lower mass triples, though a thorough study of survey biases is
needed. We show that the ARMADA survey is extremely successful at uncovering
previously unseen companions in binaries. This method will be used in upcoming
papers to constrain companion demographics in intermediate mass binary systems
down to the planetary mass regime.NASANational Science Foundation (NSF)European Research Council (ERC)Science and Technology Facilities Council (STFC)European Research Council (ERC