Spectroscopic and Spectropolarimetric Observations of V838 Monocerotis

Abstract

The spectroscopic and spectropolarimetric variability of the peculiar variable V838 Monocerotis during the brighter phases of its multiple outbursts in 2002 is presented. Significant line profile variability of H and Si ii 6347.10 and 6371.36 Å occurred in spectra obtained between 2002 February 5 and March 14, and a unique secondary absorption component was observed near the end of this time period. Our observations also suggest that multiple shifts in ionization states occurred during the outbursts. Spectropolarimetric observations reveal that V838 Mon exhibited both intrinsic and interstellar polarization components during the initial stages of the second outburst, indicating the presence of an asymmetric geometry; however, the intrinsic component had declined significantly by February 14. We determine the interstellar polarization to be P max ¼ 2:746% AE 0:011%, max ¼ 5790 AE 37 G, and P:A: ¼ 153=43 AE 0=12, and we find the integrated intrinsic V-band polarization on February 5 to be P ¼ 0:983% AE 0:012% at a position angle of 127=0 AE 0=5. The implications of these observations for the nature of V838 Monocerotis, its distance, and its ejecta are discussed.

Polarimetric evolution of V838 Monocerotis

“…3), so that the maximum could have occurred between our observations of Feb. 4 and 11, 2002. The polarization measured by Wisniewski et al (2003) on Feb. 13 is intermediate between ours on Feb. 11 and 18. Their position angle is 153…”

“…The evolution of V838 Mon from January to April 2002 is described by Munari et al (2002a). Further photometric and spectroscopic observations were presented by Kimeswenger et al (2002), Goranskii et al (2002), Kolev et al (2002), Banerjee & Ashok (2002), Wisniewski et al (2003), and Crause et al (2003). The first spectra obtained after the emersion from solar conjunction revealed a dramatic temperature decrease of the object, whose spectrum became dominated by TiO and VO molecular bands, suggesting a spectral type later than Send offprint requests to: S. Desidera, e-mail: desidera@pd.astro.it Based on observations collected at Padua Astronomical Observatory at Asiago and Crimean Astrophysical Observatory.…”

“…No depolarization was detected on Mar. 9, when H α emission was significantly fainter and the intrinsic polarization of the object was Wisniewski et al (2003) presented spectropolarimetry of V838 Mon obtained in two epochs, Feb. 8 and Feb. 13. On Feb. 8 the R-band polarization was 3.2%.…”

“…On the other hand, the presence of intrinsic polarization, its wavelength dependence, its variations during the evolution of the object and the polarization across line profiles provide clues about the physics of the object. Wisniewski et al (2003) present 2-epoch spectropolarimetric observations of V838 Mon. They reveal the presence of intrinsic polarization during the outburst, with variations across the profile of emission lines.…”

Discovery of multiple shells around V838 Monocerotis

“…After first interpretations suggested a distance of d ∼ 700 pc Kimeswenger et al 2002), subsequent revisions have led to ever increasing values for the distance of ∼2.5 kpc (Wisniewski et al 2003), > ∼ 6 kpc (Bond et al 2003) and 8 ± 2 kpc (Tylenda 2004). Early estimates supported the scenario proposed by Soker & Tylenda (2003) for the merger of two main-sequence stars, but later estimates allow for post-main-sequence scenarios.…”