Infrared Spectroscopy of Symbiotic Stars. Ix. D-Type Symbiotic Novae

Abstract

Time-series spectra of the near-infrared 1.6 μm region have been obtained for five of the six known D-type symbiotic novae. The spectra map the pulsation kinematics of the Mira component in the Mira-white dwarf binary system and provide the center-of-mass velocity for the Mira. No orbital motion is detected in agreement with previous estimates of orbital periods 100 yr and semimajor axes ∼50 AU. The 1-5 μm spectra of the Miras show line weakening during dust obscuration events. This results from scattering and continuum emission by 1000 K dust. In the heavily obscured HM Sge system the 4.6 μm CO spectrum formed in 1000 K gas is seen in emission against an optically thick dust continuum. Spectral features that are typically produced in either the cool molecular region or the expanding circumstellar region of late-type stars cannot be detected in the D-symbiotic novae. This is in accord with the colliding wind model for interaction between the white dwarf and Mira. Arguments are presented that the 1000 K gas and dust are not Mira circumstellar material but are in the wind interaction region of the colliding winds. CO is the first molecule detected in this region. We suggest that dust condensing in the intershock region is the origin of the dust obscuration. This model explains variations in the obscuration. Toward the highly obscured Mira in HM Sge the dust zone is estimated to be ∼0.1 AU thick. The intershock wind interaction zone appears thinnest in the most active systems. Drawing on multiple arguments masses are estimated for the system components. The Miras in most D-symbiotic novae have descended from intermediate mass progenitors. The large amount of mass lost from the Mira combined with the massive white dwarf companion suggests that these systems are supernova candidates. However, timescales and the number of objects make these rare events.

Very long baseline interferometry imaging of the advancing ejecta in the first gamma-ray nova V407 Cygni

“…It is thus likely that the real separation is wider, which would be in better agreement with findings based on the study of optical periodicity: for example Munari et al (1990), from a period of 43 yr, suggest 17 AU for a 1 M − 1.5 M binary (Chomiuk et al 2012) or even 20-25 AU if the red giant has a mass of 4−8 M (Nelson et al 2012). The long-term radial velocity monitoring of the Mira in V407 Cyg performed in the near-IR by Hinkle et al (2013) has failed to reveal any orbital motion superimposed to the regular pulsation; this fact is interpreted by the authors as indicative of an orbital period ≥100 years, which for M 1 + M 2 = 3 M , corresponds to a ≥31 AU (=11.5 mas).…”

“…The factors inhibiting the formation of a massive dust cocoon also in V407 Cyg probably reside in the ionisation action exerted by the accreting WD and the sweeping of the circumstellar space by the ejecta during nova outbursts. A slow modulation of the Mira brightness led Munari et al (1990) to speculate about a ≥43 yr orbital period, recently revised to the higher value of ≥100 yr by the long-term radial velocity monitoring performed by Hinkle et al (2013). V407 Cyg was first noticed when it underwent an eruption in 1936 (Hoffmeister 1949).…”

Colours of the flickering source of Mira

“…Mira AB is a very wide binary system. The infrared spectroscopy (Hinkle et al 2013) detected no orbital motion in agreement with previous estimates of the orbital period ≥ 100 yr and semimajor axes ∼ 50 au. ALMA observations revealed a mass of gas surrounding Mira B, with a size of a few tens of AU, which is interpreted as gas flowing from Mira A toward Mira B (Nhung et al 2016).…”

The GALAH survey and symbiotic stars – I. Discovery and follow-up of 33 candidate accreting-only systems

“…It is of course not precluded that a Mira pairs with a compact companion to form an SySt. For example V407 Cyg, prior to its 2010 nova outburst, was primarily studied as a Mira suffering from possible dust-obscuration episodes (Munari, Margoni & Stagni 1990;Kolotilov et al 1998) with little (or none) spectroscopic evidences for binarity (Hinkle et al 2013). Mira itself (o Cet) is a well known acc-SySt: Hubble in the ultraviolet and Chandra at X-rays have spatially resolved its WD companion, the accretion disc, and the stream fuelling it (Karovska 2006).…”