The 9 Aurigae system

Abstract

The F0 V star 9 Aur A exhibits an irregular variability of amplitude ≈0.1 magnitude at optical wavelengths. The variations are too slow for it to be a δ Scuti-type star. There is no evidence for a close, interacting companion or ring of dust, either from infrared, ultraviolet, or speckle data.

Denoising spectroscopic data by means of the improved least-squares deconvolution method

“…There is a wealth of information that can be extracted from nearly continuous micromagnitude precision photometric observations, but additional ground-based observations are essential for an accurate analysis and correct interpretation of the observed light variability. Ground-based spectroscopic observations are necessary to determine fundamental parameters like effective temperature T eff and surface gravity log g. This allows us to discriminate between slowly pulsating B (SPB, Waelkens 1991) and γ Dor (Cousins 1992;Krisciunas et al 1993;Balona et al 1994) variable stars, for example, which show the same type of variability in their light curves, but are located in different regions of the Hertzsprung-Russell (HR) diagram. Moreover, measuring the projected rotational velocity v sin i from the broadening of spectral lines helps to constrain the true rotation rate of the star, which in turn helps to interpret the observed A&A 560, A37 (2013) characteristic frequency patterns.…”

Asteroseismology of γ Doradus Variables: Past, Present, and Future

“…Future papers would identify other "variables without a cause," all with spectral types close to F0 and luminosity classes of V, IV-V, or IV. Because of their unique place in the colour-magnitude diagram [overlapping the red (cool) edge of the δ Scuti instability strip and extending to redder colours], the specific physical mechanism causing the observed variations remained a contentious subject [see Abt, Bollinger & Burke (1983); Krisciunas et al (1993);; Balona, Krisciunas & Cousins (1994); Hatzes (1998)].…”

“…Future papers would identify other "variables without a cause," all with spectral types close to F0 and luminosity classes of V, IV-V, or IV. Because of their unique place in the colour-magnitude diagram [overlapping the red (cool) edge of the δ Scuti instability strip and extending to redder colours], the specific physical mechanism causing the observed variations remained a contentious subject [see Abt, Bollinger & Burke (1983); Krisciunas et al (1993);; Balona, Krisciunas & Cousins (1994); Hatzes (1998)].Early efforts at producing a catalogue of these variables for use by the community proved to be difficult, since their discovery was usually incidental to other efforts; stars with "mistaken identities" were still catalogued, but were relegated to a "Stars Formerly Under Consideration" (SFUC) list [see, e.g., Kaye, Henry & Rodríguez (2000; misclassified δ Scuti star) and Paparó et al (2000; binary system tidal effects)]. Despite these minor setbacks, the γ Dor variables were defined as a class by Kaye et al (1999a) who, based on informal discussions at a conference held in 1995 at Cape Town, South Africa (Stobie & Whitelock 1995), and upon several papers in the literature (e.g., Krisciunas et al 1993;Balona et al 1996;Zerbi et al 1997aZerbi et al , 1997bPoretti et al 1997;Kaye 1998a;Kaye et al 1999b), defined the class to consist of "variable stars with an implied range in spectral type A7-F5 and in luminosity class IV, IV-V, or V; their variations are consistent with the model of high-order (n), low-degree ( ), nonradial, gravity-mode oscillations.…”

“…While some may suspect that this is due to the intrinsically difficult nature of analysing γ Dor data, this particular issue has been verified with double-blind tests using different software and different analytical and numerical techniques on the same sets of data. Interested readers are encouraged to examine the published literature on 9 Aurigae (see, e.g., Krisciunas et al 1991;Krisciunas et al 1993;Balona, Krisciunas & Cousins 1994; Krisciunas et al 1995a;Aerts & Krisciunas 1996;Balona et al 1996;Zerbi et al 1997a); in addition, more than 10 years of BV differential photometry is now available on this object, yet the temporal dependence of the various modes is not understood.4 The "mystery" of HD 8801 and the recently discovered similar objects are discussed in the previous section. …”

The SPECTROSCOPIC ORBITS OF FIVE Γ DORADUS STARS

“…Later, Cousins (1992) made a series of more extensive photometric observations of this early-F dwarf and determined low-amplitude variations that have periods of 0.733 and 0.757 days. Over the years, similar variables such as 9Aur (Krisciunas et al 1993), HD224638, and HD224945 (Mantegazza et al 1994) were discovered, and eventually γDor became the prototype of a new variable star class that was initially defined from the properties of 13 confirmed members by Kaye et al (1999). These objects have non-radial pulsations with periods that range from about 0.2-3 days.…”