2,250 research outputs found
In the Shadow of the Transiting Disk: Imaging epsilon Aurigae in Eclipse
Eclipses of the single-line spectroscopic binary star, epsilon Aurigae,
provide an opportunity to study the poorly-defined companion. We used the MIRC
beam combiner on the CHARA array to create interferometric images during
eclipse ingress. Our results demonstrate that the eclipsing body is a dark disk
that is opaque and tilted, and therefore exclude alternative models for the
system. These data constrain the geometry and masses of the components,
providing evidence that the F-star is not a massive supergiant star.Comment: As submitted to Nature. Published in Nature April 8, 2010
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 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 (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
The gradient flow running coupling with twisted boundary conditions
We study the gradient flow for Yang-Mills theories with twisted boundary
conditions. The perturbative behavior of the energy density is used to define a running coupling at a scale given by the
linear size of the finite volume box. We compute the non-perturbative running
of the pure gauge coupling constant and conclude that the technique is
well suited for further applications due to the relatively mild cutoff effects
of the step scaling function and the high numerical precision that can be
achieved in lattice simulations. We also comment on the inclusion of matter
fields.Comment: 27 pages. LaTe
Multiplicity of Galactic Cepheids from long-baseline interferometry. I. CHARA/MIRC detection of the companion of V1334 Cygni
This is the final version of the article. Available from the publisher via the DOI in this record.Context. More than 60% of Cepheids are in binary or multiple systems. Studying such systems could lead to a better understanding
of the age and evolution of Cepheids. These are also useful tools to estimate the mass of Cepheids, and constrain theoretical models
of their pulsation and evolution.
Aims. We aim at determining the masses of Cepheids in binary systems, as well as their geometric distances and the flux contribution
of the companions. The combination of interferometry with spectroscopy will offer a unique and independent estimate of the Cepheid
masses.
Methods. Using long-baseline interferometry at visible and infrared wavelengths, it is possible to spatially resolve binary systems
containing a Cepheid down to milliarcsecond separations. Based on the resulting visual orbit and radial velocities, we can then derive
the fundamental parameters of these systems, particularly the masses of the components and the geometric distance. We therefore
performed interferometric observations of the first-overtone mode Cepheid V1334 Cyg with the CHARA/MIRC combiner.
Results. We report the first detection of a Cepheid companion using long-baseline interferometry. We detect the signature of a
companion orbiting V1334 Cyg at two epochs. We measure a flux ratio between the companion and the Cepheid f = 3.10 ± 0.08%,
giving an apparent magnitude mH = 8.47 ± 0.15 mag. The combination of interferometric and spectroscopic data have enabled
the unique determination of the orbital elements. P = 1938.6 ± 1.2 days, Tp = 2 443 616.1 ± 7.3, a = 8.54 ± 0.51 mas, i =
124.7 ± 1.8
◦
, e = 0.190 ± 0.013, ω = 228.7 ± 1.6
◦
, and Ω = 206.3 ± 9.4
◦
. We derive a minimal distance d ∼ 691 pc, a minimum
mass for both stars of 3.6 M , with a spectral type earlier than B5.5V for the companion star. Our measured flux ratio suggests that
radial velocity detection of the companion using spectroscopy is within reach, and would provide an orbital parallax and model-free
massesThe authors would like to thank the CHARA Array and
Mount Wilson Observatory staff for their support. Research conducted at the
CHARA Array is funded by the National Science Foundation through NSF
grant AST-0908253, by Georgia State University, the W. M. Keck Foundation,
the Packard Foundation, and the NASA Exoplanet Science Institute. J.D.M.
acknowledges funding from the NSF grants AST-0707927 and AST-0807577.
W.G. and G.P. gratefully acknowledge financial support for this work from
the BASAL Centro de Astrofísica y Tecnologías Afines (CATA) PFB-06/2007.
Support from the Polish National Science Centre grant MAESTRO and the
Polish Ministry of Science grant Ideas Plus (awarded to G. P.) is also acknowledge.
This research received the support of PHASE, the high angular
resolution partnership between ONERA, Observatoire de Paris, CNRS,
and University Denis Diderot Paris 7. A.G. acknowledges support from
FONDECYT grant 3130361. LSz has been supported by the ESTEC Contract
No.4000106398/12/NL/KML. This work made use of the SIMBAD and VIZIER
astrophysical database from CDS, Strasbourg, France and the bibliographic informations
from the NASA Astrophysics Data System. This research has made
use of the Jean-Marie Mariotti Center LITpro service, co-developed by CRAL,
LAOG and FIZEAU, and SearchCal service, co-developed by FIZEAU and
LAOG/IPAG, and of CDS Astronomical Databases SIMBAD and VIZIER
Ipsilesional trajectory control is related to contralesional arm paralysis after left hemisphere damage
We have recently shown ipsilateral dynamic deficits in trajectory control are present in left hemisphere damaged (LHD) patients with paresis, as evidenced by impaired modulation of torque amplitude as response amplitude increases. The purpose of the current study is to determine if these ipsilateral deficits are more common with contralateral hemiparesis and greater damage to the motor system, as evidenced by structural imaging. Three groups of right-handed subjects (healthy controls, LHD stroke patients with and without upper extremity paresis) performed single-joint elbow movements of varying amplitudes with their left arm in the left hemispace. Only the paretic group demonstrated dynamic deficits characterized by decreased modulation of peak torque (reflected by peak acceleration changes) as response amplitude increased. These results could not be attributed to lesion volume or peak velocity as neither variable differed across the groups. However, the paretic group had damage to a larger number of areas within the motor system than the non-paretic group suggesting that such damage increases the probability of ipsilesional deficits in dynamic control for modulating torque amplitude after left hemisphere damage
Dual selection enhances the signaling specificity of a variant of the quorum-sensing transcriptional activator LuxR
Precision Orbit of δ 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 δ 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 δ Del, along with masses of 1.78 ± 0.07 M ⊙ and 1.62 ± 0.07 M ⊙ 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)
Thermal photons in QGP and non-ideal effects
We investigate the thermal photon production-rates using one dimensional
boost-invariant second order relativistic hydrodynamics to find proper time
evolution of the energy density and the temperature. The effect of
bulk-viscosity and non-ideal equation of state are taken into account in a
manner consistent with recent lattice QCD estimates. It is shown that the
\textit{non-ideal} gas equation of state i.e behaviour
of the expanding plasma, which is important near the phase-transition point,
can significantly slow down the hydrodynamic expansion and thereby increase the
photon production-rates. Inclusion of the bulk viscosity may also have similar
effect on the hydrodynamic evolution. However the effect of bulk viscosity is
shown to be significantly lower than the \textit{non-ideal} gas equation of
state. We also analyze the interesting phenomenon of bulk viscosity induced
cavitation making the hydrodynamical description invalid. We include the
viscous corrections to the distribution functions while calculating the photon
spectra. It is shown that ignoring the cavitation phenomenon can lead to
erroneous estimation of the photon flux.Comment: 11 pages, 13 figures; accepted for publication in JHE
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 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 d 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 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 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, 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 Th¨uringer 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 Union’s 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 H-band Emitting Region of the Luminous Blue Variable P Cygni: Spectrophotometry and Interferometry of the Wind
This is the final version of the article. Available from American Astronomical Society / IOP Publishing via the DOI in this record.We present the first high angular resolution observations in the near-infrared H band (1.6 μm) of the luminous blue variable star P Cygni. We obtained six-telescope interferometric observations with the CHARA Array and the MIRC beam combiner. These show that the spatial flux distribution is larger than expected for the stellar photosphere. A two-component model for the star (uniform disk) plus a halo (two-dimensional Gaussian) yields an excellent fit of the observations, and we suggest that the halo corresponds to flux emitted from the base of the stellar wind. This wind component contributes about 45% of the H-band flux and has an angular FWHM = 0.96 mas, compared to the predicted stellar diameter of 0.41 mas. We show several images reconstructed from the interferometric visibilities and closure phases, and they indicate a generally spherical geometry for the wind. We also obtained near-infrared spectrophotometry of P Cygni from which we derive the flux excess compared to a purely photospheric spectral energy distribution. The H-band flux excess matches that from the wind flux fraction derived from the two-component fits to the interferometry. We find evidence of significant near-infrared flux variability over the period from 2006 to 2010 that appears similar to the variations in the Hα emission flux from the wind.We acknowledge with thanks the variable star observations from the AAVSO International Database contributed by observers worldwide and used in this research. Support for Ritter Astrophysical Research Center during the time of the observations was provided by the National Science Foundation Program for Research and Education with Small Telescopes (NSF-PREST) under grant AST-0440784 (N.D.M.). This work was also supported by the National Science Foundation under grants AST-0606861 and AST-1009080 (D.R.G.). N.D.R. gratefully acknowledges his current CRAQ postdoctoral fellowship. We are grateful for the insightful comments of A. F. J. Moffat that improved portions of the paper, discussions with Paco Najarro and Luc Dessart about spectroscopic modeling of P Cygni, and support of the MIRC 6 telescope beam combiner by Ettore Pedretti. Institutional support has been provided by the GSU College of Arts and Sciences and by the Research Program Enhancement fund of the Board of Regents of the University System of Georgia, administered through the GSU Office of the Vice President for Research. Operational funding for the CHARA Array is provided by the GSU College of Arts and Sciences, by the National Science Foundation through grants AST-0606958 and AST-0908253, by the W. M. Keck Foundation, and by the NASA Exoplanet Science Institute. We thank the Mount Wilson Institute for providing infrastructure support at Mount Wilson Observatory. The CHARA Array, operated by Georgia State University, was built with funding provided by the National Science Foundation, Georgia State University, the W. M. Keck Foundation, and the David and Lucile Packard Foundation. This research was conducted in part using the Mimir instrument, jointly developed at Boston University and Lowell Observatory and supported by NASA, NSF, and the W. M. Keck Foundation. J.D.M. acknowledges University of Michigan and NSF AST-0707927 for support of MIRC construction and observations. D.P.C. acknowledges support under NSF AST-0907790 to Boston University. We gratefully acknowledge all of this support. This research has made use of the SIMBAD database operated at CDS, Strasbourg, France
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