[Paper Review] Rotational velocities of A-type stars II. Measurement of vsini in the northern hemisphere

F. Royer, S. Grenier+3 more|ArXiv.org|May 16, 2002

Stellar, planetary, and galactic studiesPhysics and Astronomy4 references143 citations

TL;DR

This study presents homogeneous measurements of projected rotational velocities (v sin i) for 249 A-type stars in the northern hemisphere using high-resolution spectroscopy from the OHP 1.52 m telescope. Using Fourier transform analysis of line profiles in the 4200–4600 Å range, the authors derive v sin i with a mean relative error of ~5%, confirm a systematic offset from earlier Slettebak et al. (1975) values, and establish a new calibration: v sin i(new) = 1.03 × v sin i(old) + 7.7 km s⁻¹.

ABSTRACT

This work is the second part of the set of measurements of vsini for A-type stars, begun by Royer et al. (2002). Spectra of 249 B8 to F2-type stars brighter than V=7 have been collected at Observatoire de Haute-Provence (OHP). Fourier transforms of several line profiles in the range 4200--4600 A are used to derive vsini from the frequency of the first zero. Statistical analysis of the sample indicates that measurement error mainly depends on vsini and this relative error of the rotational velocity is found to be about 5% on average. The systematic shift with respect to standard values from Slettebak et al. (1975), previously found in the first paper, is here confirmed. Comparisons with data from the literature agree with our findings: vsini values from Slettebak et al. are underestimated and the relation between both scales follows a linear law: vsini(new) = 1.03 vsini(old) + 7.7. Finally, these data are combined with those from the previous paper (Royer et al. 2002), together with the catalogue of Abt & Morrell (1995). The resulting sample includes some 2150 stars with homogenized rotational velocities.

Motivation & Objective

• To provide a homogeneous, calibration-free sample of v sin i measurements for A-type stars in the northern sky.
• To address inconsistencies in previously published v sin i values by applying a consistent, objective method.
• To quantify and correct for systematic offsets between current measurements and earlier standards (e.g., Slettebak et al. 1975).
• To combine new data with prior results (Paper I and Abt & Morrell 1995) to form a comprehensive, unified sample of ~2150 stars.
• To improve the accuracy and consistency of rotational velocity data for early-type stars used in stellar evolution and kinematic studies.

Proposed method

• Acquired high-resolution spectra (R ~ 16,000) using the AURÉLIE spectrograph on the 1.52 m telescope at Observatoire de Haute-Provence.
• Used Fourier transform techniques on line profiles in the 4200–4600 Å range to determine v sin i from the frequency of the first zero.
• Applied flat-field correction with a tungsten lamp and wavelength calibration using a Th-Ar lamp, with adjustments due to instrumental artifacts.
• Selected spectral lines in three ranges: Λ₁ (4110–4310 Å), Λ₂ (4226–4432 Å), and Λ₃ (4390–4600 Å), with Λ₃ prioritized for v sin i analysis.
• Performed sigma-clipping to identify and reject outliers when comparing with literature values, particularly for stars with known binarity or variability.
• Derived a linear scaling relation between new and old v sin i values: v sin i(new) = 1.03 × v sin i(old) + 7.7 km s⁻¹.

Experimental results

Research questions

• RQ1 What is the true distribution of v sin i for A-type stars in the northern hemisphere with minimal systematic bias?
• RQ2 How does the Fourier transform method compare to previous techniques in terms of accuracy and consistency for v sin i determination?
• RQ3 To what extent do earlier v sin i measurements (e.g., Slettebak et al. 1975) systematically underestimate true values?
• RQ4 Can a consistent, homogeneous v sin i sample be constructed by combining data from multiple sources using a common method?
• RQ5 How do stellar multiplicity and variability affect the reliability of v sin i measurements?

Key findings

• The mean relative measurement error for v sin i is approximately 5%, primarily dependent on the value of v sin i itself.
• A systematic offset is confirmed between the new measurements and those from Slettebak et al. (1975), with the latter underestimating true values.
• The linear scaling relation between old and new values is quantified as v sin i(new) = 1.03 × v sin i(old) + 7.7 km s⁻¹.
• Stars like HD 111786 and HD 192640, known to be variable or multiple systems, show significant discrepancies and were excluded from the final calibration via sigma-clipping.
• The final sample comprises ~2150 stars with homogenized v sin i values, combining data from this work, Paper I, and the Abt & Morrell (1995) catalogue.
• Vega’s v sin i is confirmed at ~23 km s⁻¹, consistent with recent high-resolution studies, rejecting earlier underestimates of <10 km s⁻¹.