SPICA, Stellar Parameters and Images with a Cophased Array: a 6T visible combiner for the CHARA array

Mourard, D.; Bério, Philippe; Perraut, K.; Clausse, J. M.; Creevey, O.; Martinod, Marc-Antoine; Meilland, A.; Millour, F.; Nardetto, N.

doi:10.1364/josaa.34.000a37

Cited by 24 publications

(14 citation statements)

References 26 publications

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“…This spectro-interferometric instrument was designed to overcome certain limitations of the VEGA instrument, as unreliable estimations of closure phase (see, e.g., . It was mainly a test instrument for the future six-telescope visible combiner SPICA at CHARA (Mourard et al 2017). Together with PAVO, mentioned above, VEGA is one of the two visible spectrointerferometric instruments on CHARA.…”

Section: The Chara Arraymentioning

confidence: 99%

Probing the weak wind phenomenon in Galactic O-type giants

Almeida

Marcolino

Bouret

et al. 2019

A&A

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Aims. Analyses of Galactic late O dwarfs (O8-O9.5V stars) raised the "weak wind problem": spectroscopic mass-loss rates (Ṁ) are up to two orders of magnitude lower than the theoretical values. We investigated the stellar and wind properties of Galactic late O giants (O8-O9.5III stars). These stars have luminosities log(L /L ) ∼ 5.2, which is the critical value (onset of weak winds) proposed in the literature. Methods. We performed a spectroscopic analysis of nine O8-O9.5III stars in the ultraviolet (UV) and optical regions using the model atmosphere code CMFGEN. Results. Stellar luminosities were adopted using calibrations from the literature. Overall, our model spectral energy distributions agree well with the observed ones considering parallaxes from the latest GAIA data release (DR2). The effective temperature derived from the UV region agrees well with the ones from the optical. As expected, the analysis of the Hertzsprung-Russell (HR) diagram shows that our sample is more evolved than late O dwarfs. From the UV region, we foundṀ ∼ 10 −8 − 10 −9 M yr -1 overall. This is lower by ∼ 0.9 − 2.3 dex than predicted values based on the (global) conservation of energy in the wind. The mass-loss rates predicted from first principles, based on the moving reversing layer theory, agree better with our findings, but it fails to match the spectroscopiċ M for the most luminous OB stars. The region of log(L /L ) ∼ 5.2 is critical for both sets of predictions in comparison with the spectroscopic mass-loss rates. CMFGEN models with the predictedṀ (the former one) fail to reproduce the UV wind lines for all the stars of our sample. We reproduce the observed Hα profiles of four objects with ourṀ derived from the UV. Hence, lowṀ values (weak winds) are favored to fit the observations (UV + optical), but discrepancies between the UV and Hα diagnostics remain for some objects. Conclusions. Our results indicate weak winds beyond the O8-9.5V class, since the region of log(L /L ) ∼ 5.2 is indeed critical to the weak wind phenomenon. Since O8-O9.5III stars are more evolved than O8-9.5V, evolutionary effects do not seem to play a role in the onset of the weak wind phenomenon. These findings support that theṀ (for low luminosity O stars) in use in the majority of modern stellar evolution codes must be severely overestimated up to the end of the H-burning phase. Further investigations must evaluate the consequences of weak winds in terms of physical parameters for massive stars (e.g., angular momentum and CNO surface abundances).

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Section: The Chara Arraymentioning

confidence: 99%

Probing the weak wind phenomenon in Galactic O-type giants

Almeida

Marcolino

Bouret

et al. 2019

A&A

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“…The S/N in the power spectrum of the interferogram has been already modeled by different authors (Gordon & Buscher 2012;Mourard et al 2017). As previously said, we use an improved model of the photon noise for an EMCCD, including dark current and CIC, by using the expression σ 2 mod presented in Eq.…”

Section: On-sky S/n On Vmentioning

confidence: 99%

Fibered visible interferometry and adaptive optics: FRIEND at CHARA

Martinod

Mourard

Bério

et al. 2018

A&A

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Aims. In the context of the future developments of long baseline interferometry at visible wavelengths, we have built a prototype instrument called Fibered spectrally Resolved Interferometer -New Design (FRIEND) based on single mode fibers and a new generation detector called Electron Multiplying Charge-Coupled Device (EMCCD). Installed on the Center for High Angular Resolution Astronomy (CHARA) array, it aims to estimate the performance of a fibered instrument in the visible when coupled with telescopes equipped with adaptive optics (AO) in partial correction. Methods. We observed different sequences of targets and reference stars to study the compensation of the birefringence of the fibers, the coupling efficiency in various conditions of correction, and to calibrate our numerical model of signal-to-noise ratio (S/N). We also used a known binary star to demonstrate the reliability and the precision of our squared visibility and closure phase measurements. Results. We firstly present a reliable and stable solution for compensating the birefringence of the fibers with an improvement of a factor of 1.5 of the instrumental visibility. We then demonstrate an improvement by a factor of between 2.5 and 3 of the coupling efficiency when using the LABAO systems in closed loop. The third results of our paper is the demonstration of the correct calibration of the parameters of our S/N estimator provided the correct excess noise factor of EMCCD is correctly taken into account. Finally with the measurements of the angular separation, difference of magnitude and individual diameters of the two components of ζ Ori A, we demonstrate the reliability and precision of our interferometric estimators, and in particular a median residual on the closure phase of 1.2• .

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“…Next generation combiners like MYSTIC (K-band) and SPICA (visible, Mourard et al 2017) are also being planned/discussed. NPOI will be adding 1-m telescopes to improve throughput.…”

Section: Planet Formationmentioning

confidence: 99%

A recent history of science cases for optical interferometry

Defrère

Aerts²,

Kishimoto

et al. 2018

Exp Astron

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Optical long-baseline interferometry is a unique and powerful technique for astronomical research. Since the 1980's (with I2T, GI2T, Mark I to III, SUSI, ...), optical interferometers have produced an increasing number of scientific papers covering various fields of astrophysics. As current interferometric facilities are reaching their maturity, we take the opportunity in this paper to summarize the conclusions of a few key meetings, workshops, and conferences dedicated to interferometry. We present the most persistent recommendations related to science cases and discuss some key technological developments required to address them. In the era of extremely large telescopes, optical long-baseline interferometers will remain crucial to probe the smallest spatial scales and make breakthrough discoveries.

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SPICA, Stellar Parameters and Images with a Cophased Array: a 6T visible combiner for the CHARA array

Cited by 24 publications

References 26 publications

Probing the weak wind phenomenon in Galactic O-type giants

Probing the weak wind phenomenon in Galactic O-type giants

Fibered visible interferometry and adaptive optics: FRIEND at CHARA

A recent history of science cases for optical interferometry

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