Taking the Measure of Massive Stars and their Environments with the CHARA Array Long-baseline Interferometer

AbstractMost massive stars are so distant that their angular diameters are too small for direct resolution. However, the observational situation is now much more favorable, thanks to new opportunities available with optical/IR long-baseline interferometry. The Georgia State University Center for High Angular Resolution Astronomy Array at Mount Wilson Observatory is a six-telescope instrument with a maximum baseline of 330 meters, which is capable of resolving stellar disks with diameters as small as 0.2 milliarcsec. The distant stars are no longer out of range, and many kinds of investigations are possible. Here we summarize a number of studies involving angular diameter measurements and effective temperature estimates for OB stars, binary and multiple stars (including the σ Orionis system), and outflows in Luminous Blue Variables. An enlarged visitors program will begin in 2017 that will open many opportunities for new programs in high angular resolution astronomy.

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High Angular Resolution Studies of Binaries at Georgia State University

Active Close Binaries ◽

10.1007/978-94-009-0679-2_51 ◽

1990 ◽

pp. 729-736 ◽

Cited By ~ 1

Author(s):

Donald J. Barry

Keyword(s):

Angular Resolution ◽

High Angular Resolution ◽

State University ◽

Georgia State University

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INTRODUCTION

Journal of Astronomical Instrumentation ◽

10.1142/s2251171713030013 ◽

2013 ◽

Vol 02 (02) ◽

pp. 1303001 ◽

Cited By ~ 1

Author(s):

T. TEN BRUMMELAAR ◽

P. TUTHILL ◽

G. VAN BELLE

Keyword(s):

Near Infrared ◽

Angular Resolution ◽

The United States ◽

High Angular Resolution ◽

State University ◽

Observational Astronomy ◽

Georgia State University ◽

Infrared Interferometry ◽

Optical Astronomy ◽

Modern Instrumentation

After nearly one and a half centuries of effort, one of the most pernicious problems in observational astronomy — obtaining resolved images of the stars — is finally yielding to advances in modern instrumentation. The exquisite precision delivered by today's interferometric observatories is rapidly being applied to more and more branches of optical astronomy. The most capable interferometers in the Northern Hemisphere, both located in the United States are the Navy Precision Optical Interferometer (NPOI) in Arizona and the Center for High Angular Resolution Astronomy Array (CHARA) run by Georgia State University and located in California. In early 2013 these two groups held a joint meeting hosted by the Lowell Observatory in Flagstaff. All major groups working in the field were represented at this meeting and it was suggested to us by this Journal that this was an excellent opportunity to put together a special issue on interferometry. In order to be as broad as possible, those who did not attend the CHARA/NPOI meeting were also solicited to make a contribution. The result is this collection of papers representing a snap shot of the state of the art of ground based optical and near infrared interferometry.

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Constraining VLBI−optical offsets in high redshift galaxies using strong gravitational lensing

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa870 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2312-2326 ◽

Cited By ~ 3

Author(s):

Cristiana Spingola ◽

Anna Barnacka

Keyword(s):

Gravitational Lensing ◽

Angular Resolution ◽

Hubble Space Telescope ◽

High Redshift ◽

Monte Carlo Sampling ◽

High Angular Resolution ◽

Radio Emissions ◽

High Redshift Galaxies ◽

Long Baseline ◽

Redshift Galaxies

ABSTRACT We present a multiwavelength analysis of two highly magnified strong gravitationally lensed galaxies, CLASS B0712+472 and CLASS B1608+656, at redshifts 1.34 and 1.394, respectively, using new VLBI (very long baseline interferometry) and archival Hubble Space Telescope observations. We reconstruct the positions of the radio and optical emissions with their uncertainties using Monte Carlo sampling. We find that in CLASS B0712+472 the optical and radio emissions are co-spatial within 2 ± 5 mas (17 ± 42 pc at redshift of 1.34). But, in CLASS B1608+656, we reconstruct an optical–radio offset of 25 ± 16 mas (214 ± 137 pc at redshift of 1.394), among the smallest offsets measured for an AGN (active galactic nucleus) at such high redshift. The spectral features indicate that CLASS B1608+656 is a post-merger galaxy, which, in combination with the optical–VLBI offset reported here, makes CLASS B1608+656 a promising candidate for a high- z offset–AGN. Furthermore, the milliarcsecond angular resolution of the VLBI observations combined with the precise lens models allow us to spatially locate the radio emission at 0.05 mas precision (0.4 pc) in CLASS B0712+472, and 0.009 mas precision (0.08 pc) in CLASS B1608+656. The search for optical–radio offsets in high redshift galaxies will be eased by the upcoming synoptic all-sky surveys, including Extremely Large Telescope and Square Kilometre Array, which are expected to find ∼105 strongly lensed galaxies, opening an era of large strong lensing samples observed at high angular resolution.

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Water masers and the near-stellar environment in YSOs

Symposium - International Astronomical Union ◽

10.1017/s0074180900222006 ◽

2002 ◽

Vol 206 ◽

pp. 27-34

Author(s):

Mark J. Claussen

Keyword(s):

Main Sequence ◽

Very Long Baseline Interferometry ◽

Angular Resolution ◽

Young Stellar Objects ◽

High Angular Resolution ◽

High Luminosity ◽

Stellar Objects ◽

Long Baseline ◽

Water Masers ◽

Very High

I present a review of observations of water masers, in particular very high angular resolution of water masers using Very Long Baseline Interferometry, with which it is possible to probe the environment of young stellar objects and forming stars within only a few A.U. of the protostar, its accretion disk, and therefore the base of outflowing material. Although reference is made to some high-luminosity sources, the main thrust of the review are the water masers found toward forming objects whose mass and luminosity will be approximately that of the Sun when they reach the main sequence.

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Interferometry and Stellar Magnetism

International Astronomical Union Colloquium ◽

10.1017/s0252921100055792 ◽

2000 ◽

Vol 175 ◽

pp. 174-177 ◽

Cited By ~ 1

Author(s):

O. Chesneau ◽

K. Rousselet-Perraut ◽

F. Vakili

Keyword(s):

Spectral Resolution ◽

Angular Resolution ◽

Zeeman Effect ◽

High Spectral Resolution ◽

Sensitivity Threshold ◽

High Angular Resolution ◽

Be Stars ◽

Long Baseline ◽

Instrumental Polarisation ◽

Very High

AbstractThe classical detection of magnetic fields in Be stars remains a challenge due to the sensitivity threshold and geometrical cancelation of the field effects. We propose to study the Zeeman effect using Spectro-Polarimetric INterferometry (SPIN) which consists of the simultaneous use of polarimetry and very high angular resolution provided by long baseline interferometers. As monitoring of the instrumental polarisation is mandatory in order to calibrate interferometric observations in any case, the polarised signal is a natural by-product of interferometers. This method will be tested on the GI2T interferometer thanks to its high spectral resolution and its polarimetric capabilities.

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VLBI from the Moon

Highlights of Astronomy ◽

10.1017/s1539299600019377 ◽

1998 ◽

Vol 11 (2) ◽

pp. 985-987

Author(s):

L. I. Gurvits

Keyword(s):

Radio Astronomy ◽

Very Long Baseline Interferometry ◽

Angular Resolution ◽

High Angular Resolution ◽

The Moon ◽

Next Generation ◽

Space Observatory ◽

Long Baseline ◽

The Earth ◽

The Universe

Very Long Baseline Interferometry (VLBI) technique occupies a special place among tools for studying the Universe due to its record high angular resolution. The latter is in the inverse proportion to the length of interferometer baseline at any given wavelength. Until recently, the available angular resolution in radio domain of about 1 milliarcsecond at centimeter wavelengths was limited by the diameter of the Earth. However, many astrophysical problems require a higher angular resolution. The only way to achieve this at a given wavelength is to create an interferometer with the baseline larger than the Earth’s diameter by placing at least one telescope in space. In February 1997, the first dedicated Space VLBI mission, VLBI Space Observatory Program (VSOP), led by the Institute of Space and Astronautical Sciences (Japan) has been launched (Hirabayashi 1997). The VSOP mission opens a new dimension in the development of radio astronomy of extremely high angular resolution and will be followed by other Space VLBI missions. A review of scientific drives and technological challenges of the next generation Space VLBI mission have been discussed, for example, by Gurvits et al. (1996) and Ulvestad et al. (1997).

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Michelson-Spectro-Interferometry (MSI) of Be stars envelopes with the GI2T Interferometer

International Astronomical Union Colloquium ◽

10.1017/s0252921100023320 ◽

1995 ◽

Vol 149 ◽

pp. 365-368

Author(s):

Ph. Stee ◽

D. Bonneau ◽

P. Lawson ◽

F. Morand ◽

D. Mourard ◽

...

Keyword(s):

Angular Resolution ◽

Michelson Interferometer ◽

Numerical Code ◽

High Angular Resolution ◽

Be Stars ◽

Wind Model ◽

Long Baseline ◽

Balmer Lines ◽

Extended Sources ◽

Resolution Data

AbstractThe GI2T is an optical long-baseline Michelson interferometer which analyses dispersed stellar fringes in the multi-speckle mode with a spectral resolution of one Angstrom while the spatial resolution is about one milliarcsecond. This makes the GI2T a powerful instrument able to perform MSI of extended sources like Be stars or shell stars. In order to interpret these data we have developed a latitude dependent radiative wind model for Be stars. This numerical code enables us to compare directly computed 2D maps in some Balmer lines (Hα and Hβ) with high angular resolution data of some Be stars.

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Infrared Long Baseline Interferometry

Highlights of Astronomy ◽

10.1017/s1539299600008352 ◽

1989 ◽

Vol 8 ◽

pp. 563-564

Author(s):

W.C. Danchi ◽

M. Bester ◽

P.R. McCullough ◽

C.H. Townes

Keyword(s):

Delay Line ◽

Angular Resolution ◽

Spectral Characteristics ◽

High Angular Resolution ◽

Mid Infrared ◽

Long Baseline ◽

Interference Fringes ◽

Infrared Spectral ◽

New Instruments ◽

Hgcdte Photodiodes

During the last few years, two new instruments using long baseline interferometry have been constructed for high angular resolution astronomy in the mid-infrared spectral region (8-12 μxm). One called SOIRDETE-Synthese d’Overture en InfraRouge a DEux TElescopes-was built by J. Gay and his collaborators at CERGA. SOIRDETE has a fixed E-W 15 m baseline and two 1 m diameter telescopes of conventional design. This instrument obtains interference fringes by adjusting an optical-precision delay line in discrete steps to compensate for the geometrical delay of the projected baseline. The interference fringe from the source is detected using HgCdTe photodiodes. Because the instrumental delay has discrete steps a time-domain interferogram is created. This interferogram, upon Fourier transformation to the frequency domain, yields information about the spectral characteristics of the source. First fringes have recently been obtained with this instrument (Gay, 1988).

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