The unusual pre-main-sequence star V718 Persei (HMW 15)

Abstract

Context. The remarkable pre-main-sequence object V718 Per (HMW 15, H187) in the young cluster IC 348 periodically undergoes long-lasting eclipses caused by variable amounts of circumstellar dust in the line-of-sight to the star. It has been speculated that the star is a close binary and similar to another unusual eclipsing object, KH 15D. Aims. We have submitted V718 Per to a detailed photometric and spectroscopic study to investigate how regular the recurrent eclipses are, to find out more about the properties of the stellar object and the occulting circumstellar material, and to look for signatures of a possible binary component. Methods. V718 Per was monitored photometrically from the optical to the near-infrared (NIR). We also obtained high-resolution optical spectra with the Keck telescope at minimum as well as at maximum brightness. We derived the fundamental photospheric parameters of this star by comparing with synthetic spectra. Results. Our photometric data show that the eclipses are very symmetric and persistent, and that the extinction law of the foreground occulting dust deviates only little from what is expected for "normal" interstellar material. The stellar parameters of V718 Per indicate a primordial abundance of Li and a surface temperature of T eff ≈ 5200 K. Remarkably, the in-eclipse spectrum shows a significant broadening of the photospheric absorption lines, as well as a slightly lower stellar surface temperature. In addition, weak emission components appear in the absorption lines of Hα and the Ca II IR triplet lines. We did not detect any signs of atomic or molecular features related to the occulting body in the in-eclipse spectrum. We also found no evidence of any radial velocity changes in V718 Per to within about ±80 m s −1 , which for an edge-on system corresponds to a maximum companion mass of ∼6 M Jup . Conclusions. Our observations suggest that V718 Per is a single star, and thus very different from the related binary system KH 15D. We conclude that V718 Per is surrounded by an edge-on circumstellar disk with an irregular mass distribution orbiting at a distance of 3.3 AU from the star, presumably at the inner disk edge. To produce the prolonged eclipses, the occulting feature must extend along more than half of the inner disk edge. The change in stellar surface temperature and the emission line activity observed could be related to spot activity. We ascribe the broadening of photospheric absorption lines during the eclipse to forward scattering of stellar light in the circumstellar dust feature.

An unusual very low-mass high-amplitude pre-main sequence periodic variable

“…In the following, on the basis of the observations of V718 Per (Grinin et al 2006(Grinin et al , 2008Herbst et al 2010b), we argue that single periodically variable PMS stars with large variation amplitudes can be explained by strong absorption in their circumstellar discs over large fractions of their orbit.…”

Another deep dimming of the classical T Tauri star RW Aurigae A

“…We note that a few other weak-line TTS have shown longer eclipses by foreground dust (see e.g. Grinin et al 2008;Mamajek et al 2012).…”

Flares of accretion activity of the 20 Myr old UXOR RZ Psc

“…4). Such an effect was predicted in the theoretical work by Grinin et al (2006) and observed in another unusual pre-main-sequence star V718 Per (Grinin et al 2008). According to their model, the broadening of the photospheric lines in the spectra of young T Tauri stars occurs due to the Doppler scattering of the stellar radiation on the moving dust particles in the inner regions of the circumstellar discs.…”