Normal A0−A1 stars with low rotational velocities

Royer, F.; Gebran, M.; Monier, Richard; Adelman, Saul J.; Smalley, B.; Pintado, O. I.; Reiners, A.; Hill, Graham; Gulliver, A. F.

doi:10.1051/0004-6361/201322762

Cited by 28 publications

(54 citation statements)

References 56 publications

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“…Royer et al (2014) suspected that this star could be a binary system as the cross-correlation function has an asymmetric profile. Figure 7 shows the profile of several lines in the SOPHIE spectrum of HD 6530.…”

Section: Hd 6530mentioning

confidence: 99%

A new method for the inversion of atmospheric parameters of A/Am stars

Gebran

Farah

Paletou

et al. 2016

A&A

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Context. We present an automated procedure that simultaneously derives the effective temperature T eff , surface gravity log g, metallicity [Fe/H], and equatorial projected rotational velocity v sin i for "normal" A and Am stars. The procedure is based on the principal component analysis (PCA) inversion method, which we published in a recent paper . Aims. A sample of 322 high-resolution spectra of F0-B9 stars, retrieved from the Polarbase, SOPHIE, and ELODIE databases, were used to test this technique with real data. We selected the spectral region from 4400−5000 Å as it contains many metallic lines and the Balmer Hβ line. Methods. Using three data sets at resolving powers of R = 42 000, 65 000 and 76 000, about ∼6.6 × 10 6 synthetic spectra were calculated to build a large learning database. The online power iteration algorithm was applied to these learning data sets to estimate the principal components (PC). The projection of spectra onto the few PCs offered an efficient comparison metric in a low-dimensional space. The spectra of the well-known A0-and A1-type stars, Vega and Sirius A, were used as control spectra in the three databases. Spectra of other well-known A-type stars were also employed to characterize the accuracy of the inversion technique. Results. We inverted all of the observational spectra and derived the atmospheric parameters. After removal of a few outliers, the PCA-inversion method appeared to be very efficient in determining T eff , [Fe/H], and v sin i for A/Am stars. The derived parameters agree very well with previous determinations. Using a statistical approach, deviations of around 150 K, 0.35 dex, 0.15 dex, and 2 km s −1 were found for T eff , log g, [Fe/H], and v sin i with respect to literature values for A-type stars. Conclusions. The PCA inversion proves to be a very fast, practical, and reliable tool for estimating stellar parameters of FGK and A stars and for deriving effective temperatures of M stars.

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Section: Hd 6530mentioning

confidence: 99%

A new method for the inversion of atmospheric parameters of A/Am stars

Gebran

Farah

Paletou

et al. 2016

A&A

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“…These seven stars have spectral types ranging from A0 to A7. Merak also has a peculiar metallicity (Royer et al 2014) and is an apparent slow rotator with a v i sin of 46 ± 2.3 km s .…”

Section: The Sample and Chara Observationsmentioning

confidence: 99%

The Ages of a-Stars. I. Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group

Jones

White

Boyajian

et al. 2015

ApJ

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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 (v i sin  170 km s 1 -) and are expected to be oblate. These interferometric measurements, the stars' observed photometric energy distributions, and v i sin 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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“…These various expressions refer to two main difficulties. First, δ Scuti stars, as chemically normal A and early F stars are characterized by a large rotation rate ( [5]) and the theoretical modelling of their pulsation spectra cannot rely on classical perturbative approaches ( [6], [7]). Then, although we understand the process responsible for their pulsational instability, we have very little insight about the process responsible for the amplitude limitation (see however recent studies by [8] and [9]) and thus no clue about how amplitudes are distributed between modes and for different stars.…”

Section: Introductionmentioning

confidence: 99%

What CoRoT tells us about δ Scuti stars

Michel¹,

Dupret²,

Reese³

et al. 2017

EPJ Web Conf.

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Abstract. Inspired by the so appealing example of red giants, where going from a handful of stars to thousands revealed the structure of the eigenspectrum, we inspected a large homogeneous set of around 1860 δ Scuti stars observed with CoRoT. This unique data set reveals a common regular pattern which appears to be in agreement with island modes featured by theoretical non-perturbative treatments of fast rotation. The comparison of these data with models and linear stability calculations suggests that spectra can be fruitfully characterized to first order by a few parameters which might play the role of seismic indices for δ Scuti stars, as ∆ν and ν max do for red giants. The existence of this pattern offers an observational support for guiding further theoretical works on fast rotation. It also provides a framework for further investigation of the observational material collected by CoRoT ([1]) and Kepler ([2]). Finally, it sketches out the perspective of using δ Scuti stars pulsations for ensemble asteroseismology.

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Normal A0−A1 stars with low rotational velocities

Cited by 28 publications

References 56 publications

A new method for the inversion of atmospheric parameters of A/Am stars

A new method for the inversion of atmospheric parameters of A/Am stars

The Ages of a-Stars. I. Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group

What CoRoT tells us about δ Scuti stars

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