The CHARA Array is a six 1 m telescope optical/IR interferometric array located on Mount Wilson, California, designed and built by the Center for High Angular Resolution Astronomy of Georgia State ...University. In this paper we describe the main elements of the Array hardware and software control systems, as well as the data reduction methods currently being used. Our plans for upgrades in the near future are also described.
We have measured the angular diameters of six M dwarfs with the CHARA Array, a long-baseline optical interferometer located at Mount Wilson Observatory. Spectral types range from M1.0 V to M3.0 V and ...linear radii from 0.38 to 0.69 R sub( ). These results are consistent with the seven other M dwarf radii measurements from optical interferometry and with those for 14 stars in eclipsing binary systems. We compare all directly measured M dwarf radii to model predictions and find that current models underestimate the true stellar radii by up to 15%-20%. The differences are small among the metal-poor stars but become significantly larger with increasing metallicity. This suggests that theoretical models for low-mass stars may be missing some opacity source that alters the computed stellar radii.
We present the results of long-baseline optical interferometry observations using the Precision Astronomical Visual Observations (PAVO) beam combiner at the Center for High Angular Resolution ...Astronomy (CHARA) Array to measure the angular sizes of three bright Kepler stars: θ Cygni, and both components of the binary system 16 Cygni. Supporting infrared observations were made with the Michigan Infrared Combiner (MIRC) and Classic beam combiner, also at the CHARA Array. We find limb-darkened angular diameters of 0.753 ± 0.009 mas for θ Cyg, 0.539 ± 0.007 mas for 16 Cyg A and 0.490 ± 0.006 mas for 16 Cyg B. The Kepler Mission has observed these stars with outstanding photometric precision, revealing the presence of solar-like oscillations. Due to the brightness of these stars the oscillations have exceptional signal-to-noise, allowing for detailed study through asteroseismology, and are well constrained by other observations. We have combined our interferometric diameters with Hipparcos parallaxes, spectrophotometric bolometric fluxes and the asteroseismic large frequency separation to measure linear radii (θ Cyg: 1.48 ± 0.02 R, 16 Cyg A: 1.22 ± 0.02 R, 16 Cyg B: 1.12 ± 0.02 R), effective temperatures (θ Cyg: 6749 ± 44 K, 16 Cyg A: 5839 ± 42 K, 16 Cyg B: 5809 ± 39 K) and masses (θ Cyg: 1.37 ± 0.04 M, 16 Cyg A: 1.07 ± 0.05 M, 16 Cyg B: 1.05 ± 0.04 M) for each star with very little model dependence. The measurements presented here will provide strong constraints for future stellar modelling efforts.
Abstract Congenital insensitivity to pain (CIP) comprises the rare heritable disorders without peripheral neuropathy that feature inability to feel pain. Fracturing and joint destruction are common ...complications, but lack detailed studies of mineral and skeletal homeostasis and bone histology. In 2013, discovery of a heterozygous gain-of-function mutation in SCN11A encoding voltage-gated sodium channel 1.9 (Nav 1.9) established a distinctive CIP in three unrelated patients who suffered multiple painless fractures, self-inflicted mutilation, chronic diarrhea, and hyperhidrosis. Here, we studied a mother and two children with CIP by physical examination, biochemical testing, radiological imaging including DXA, iliac crest histology, and mutation analysis. She suffered fractures primarily of her lower extremities beginning at age two years, and had Charcot deformity of both ankles and joint hypermobility. Nerve conduction velocity together with electromyography were normal. Her children had recurrent major fractures beginning in early childhood, joint hypermobility, and chronic diarrhea. She had an excoriated external nare, and both children had hypertrophic scars from scratching. Skin collagen studies were normal. Radiographs revealed fractures and deformities. However, lumbar spine and total hip BMD Z-scores, biochemical parameters of mineral and skeletal homeostasis, and iliac crest histology of the mother (after in vivo tetracycline labeling) were normal. Genomic DNA from the children revealed a unique heterozygous missense mutation in exon 23 (c.3904C > T, p.Leu1302Phe) of SCN11A that is absent in SNP databases and alters an evolutionarily conserved amino acid. This autosomal dominant CIP reflects the second gain-of-function mutation of SCN11A . Perhaps joint hypermobility is an unreported feature. How mutation of Nav 1.9 causes fracturing remains unexplained. Lack of injury awareness is typically offered as the reason, and was supported by our unremarkable biochemical, radiological, and histological findings indicating no skeletal pathobiology. However, low-trauma fracturing in these patients suggests an uncharacterized defect in bone quality.
We have obtained high-precision interferometric measurements of Vega with the CHARA Array and FLUOR beam combiner in the K' band at projected baselines between 103 and 273 m. The measured visibility ...amplitudes beyond the first lobe are significantly weaker than expected for a slowly rotating star characterized by a single effective temperature and surface gravity. Our measurements, when compared to synthetic visibilities and synthetic spectrophotometry from a Roche-von Zeipel gravity-darkened model atmosphere, provide strong evidence for the model of Vega as a rapidly rotating star viewed very nearly pole-on. Our best-fitting model indicates that Vega is rotating at 691% of its angular break-up rate with an equatorial velocity of 275 km s super(-1). Together with the measured v sin i, this velocity yields an inclination for the rotation axis of 5. For this model the pole-to-equator effective temperature difference is 62250 K, a value much larger than previously derived from spectral line analyses. A polar effective temperature of 10,150 K is derived from a fit to ultraviolet and optical spectrophotometry. The synthetic and observed spectral energy distributions are in reasonable agreement longward of 140 ran, where they agree to 5% or better. Shortward of 140 ran, the model is up to 10 times brighter than observed. The model has a luminosity of 637 L , a value 35% lower than Vega's apparent luminosity based on its bolometric flux and parallax, assuming a slowly rotating star. Our model predicts the spectral energy distribution of Vega as viewed from its equatorial plane, and it may be employed in radiative models for the surrounding debris disk.
Imaging the Surface of Altair Monnier, John D; Zhao, M; Pedretti, E ...
Science (American Association for the Advancement of Science),
07/2007, Volume:
317, Issue:
5836
Journal Article
Peer reviewed
Open access
Spatially resolving the surfaces of nearby stars promises to advance our knowledge of stellar physics. Using optical long-baseline interferometry, we constructed a near-infrared image of the rapidly ...rotating hot star Altair with a resolution of <1 milliarcsecond. The image clearly reveals the strong effect of gravity darkening on the highly distorted stellar photosphere. Standard models for a uniformly rotating star cannot explain our findings, which appear to result from differential rotation, alternative gravity-darkening laws, or both.
We present results of a long-baseline interferometry campaign using the PAVO beam combiner at the CHARA Array to measure the angular sizes of five main-sequence stars, one subgiant and four red giant ...stars for which solar-like oscillations have been detected by either Kepler or CoRoT. By combining interferomettic angular diameters, Hipparcos parallaxes, asteroseismic densities, bolometric fluxes, and high-resolution spectroscopy, we derive a full set of near-model-independent fundamental properties for the sample. We first use these properties to test asteroseismic scaling relations for the frequency of maximum power (v sub(max)) and the large frequency separation ( Delta v). We find excellent agreement within the observational uncertainties, and empirically show that simple estimates of asteroseismic radii for main-sequence stars are accurate to lap4%. We furthermore find good agreement of our measured effective temperatures with spectroscopic and photometric estimates with mean deviations for stars between T sub(eff) = 4600-6200 K of -22 + or - 32 K (with a scatter of 97 K) and -58 + or - 31 K (with a scatter of 93 K), respectively. Finally, we present a first comparison with evolutionary models, and find differences between observed and theoretical properties for the metal-rich main-sequence star HD 173701. We conclude that the constraints presented in this study will have strong potential for testing stellar model physics, in particular when combined with detailed modeling of individual oscillation frequencies.
ABSTRACT We have observed and spatially resolved a set of seven A-type stars in the nearby Ursa Major moving group with the Classic, CLIMB, and PAVO beam combiners on the Center for High Angular ...Resolution Astronomy Array. At least four of these stars have large rotational velocities ( 170 ) and are expected to be oblate. These interferometric measurements, the stars' observed photometric energy distributions, and values are used to computationally construct model oblate stars from which stellar properties (inclination, rotational velocity, and the radius and effective temperature as a function of latitude, etc.) are determined. The results are compared with MESA stellar evolution models to determine masses and ages. The value of this new technique is that it enables the estimation of the fundamental properties of rapidly rotating stars without the need to fully image the star. It can thus be applied to stars with sizes comparable to the interferometric resolution limit as opposed to those that are several times larger than the limit. Under the assumption of coevality, the spread in ages can be used as a test of both the prescription presented here and the MESA evolutionary code for rapidly rotating stars. With our validated technique, we combine these age estimates and determine the age of the moving group to be 414 23 Myr, which is consistent with, but much more precise than previous estimates.
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