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Near-IR Observations of V1500 Cyg, and WISE Data

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Near-IR Observations of V1500 Cyg, and WISE Data The Astronomical Journal, 146:37 (18pp), 2013 August doi:10.1088/0004-6256/146/2/37 C 2013. The American Astronomical Society. All rights reserved. Printed in the U.S.A. PHASE-RESOLVED INFRARED SPECTROSCOPY AND PHOTOMETRY OF V1500 CYGNI, AND A SEARCH FOR SIMILAR OLD CLASSICAL NOVAE Thomas E. Harrison1,3,4, Randy D. Campbell2, and James E. Lyke2 1 Department of Astronomy, New Mexico State University, Box 30001, MSC 4500, Las Cruces, NM 88003-8001, USA; [email protected] 2 W. M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743, USA; [email protected], [email protected] Received 2013 March 22; accepted 2013 June 5; published 2013 July 12 ABSTRACT We present phase-resolved near-infrared photometry and spectroscopy of the classical nova (CN) V1500 Cyg to explore whether cyclotron emission is present in this system. While the spectroscopy do not indicate the presence of discrete cyclotron harmonic emission, the light curves suggest that a sizable fraction of its near-infrared fluxes are due to this component. The light curves of V1500 Cyg appear to remain dominated by emission from the heated face of the secondary star in this system. We have used infrared spectroscopy and photometry to search for other potential magnetic systems among old CNe. We have found that the infrared light curves of V1974 Cyg superficially resemble those of V1500 Cyg, suggesting a highly irradiated companion. The old novae V446 Her and QV Vul have light curves with large amplitude variations like those seen in polars, suggesting they might have magnetic primaries. We extract photometry for 79 old novae from the Two Micron All Sky Survey Point Source Catalog and use those data to derive the mean, un-reddened infrared colors of quiescent novae. We also extract WISE data for these objects and find that 45 of them were detected. Surprisingly, a number of these systems were detected in the WISE 22 μm band. While two of those objects produced significant dust shells (V705 Cas and V445 Pup), the others did not. It appears that line emission from their ionized ejected shells is the most likely explanation for those detections. Key words: infrared: stars – novae, cataclysmic variables Online-only material: color figures 1. INTRODUCTION to originate from processes occurring near the magnetic poles of the rapidly rotating white dwarfs in these systems. In po- Classical novae (CNe) eruptions are thermonuclear runaways lars, the stronger field captures the accretion stream close to (TNR) on the surface of a white dwarf that has been accreting the secondary star and funnels it onto the magnetic poles of the material from a low mass companion for millennia. Townsley & white dwarf. Both the primary and secondary stars in polars are Bildsten (2004) show that for systems with mass accretion rates phase-locked to rotate at the orbital period. ˙ −8 −10 −1 of M = 10 to 10 M yr , ignition of the TNR can occur That there are magnetic CVs among the old novae is already once the accumulated envelope on the white dwarf exceeds well known with such famous CNe such as DQ Her, V603 Aql, −5 10 M. The resulting eruption can surpass the Eddington and GK Per being classified as IPs. Whether there are true polars −4 limit, and eject ≈10 M of nuclear processed material at among the CNe has not yet been fully answered. The best case high velocity. The eruptions of CNe provide tests of our for the latter is V1500 Cyg. Stockman et al. (1988)showed understanding of TNRs, the nucleosynthesis that occurs within that V1500 Cyg exhibits strong, orbitally modulated circular the burning layers (e.g., Starrfield et al. 2009), and the factors polarization that they suggested comes from high-harmonic that drive the outburst luminosity and shell ejection process cyclotron emission. V1500 Cyg is slightly asynchronous, so (e.g., Shaviv 2001). it is not currently a true polar, but Schmidt & Stockman All CNe are cataclysmic variables (CVs). CVs can be sep- (1991) suggest it will return to synchronism within ∼150 yr. arated into two broad classes: magnetic and non-magnetic. Another likely highly magnetic CN is V2214 Oph. Baptista Magnetic CVs harbor white dwarfs that have field strengths et al. (1993) compare its visual light curve to the proto-type polar of B>1 MG, while the field strengths for the white dwarfs AM Her (Crampton & Cowley 1977; Campbell et al. 2008a). in non-magnetic CVs are believed to be considerably smaller The similarity is striking, and it is difficult to envision how such (though see Warner 2004). In addition, magnetic CVs are further a light curve could be produced by a source other than cyclotron subdivided into two subclasses: polars and intermediate polars emission. (IPs). IPs are believed to have lower magnetic field strengths V1500 Cyg was a remarkable CN, having one of the largest (B 7 MG) than polars. IPs are identified by having coherent outburst amplitudes (Δm ∼ 19.2 mag; Warner 1985), and one periodicities that are shorter than their orbital periods, believed of the most rapid declines from visual maximum ever observed (t3 = 3.7 days; Downes & Duerbeck 2000; Strope et al. 2010). 3 Expansion parallax measures give a distance of 1.5 kpc (Slavin Visiting Observer, W. M. Keck Observatory, which is operated as a scientific et al. 1995) to V1500 Cyg, and thus an absolute magnitude at partnership among the California Institute of Technology, the University of =− California, and the National Aeronautics and Space Administration. NOAO maximum of MVmax 10.7. The only other CN that rivals this proposal 2006A-0005. luminosity is CP Pup, an object that Warner (1985) shows has 4 Visiting Astronomer, Kitt Peak National Observatory, National Optical acted in a similar fashion to V1500 Cyg. Both of these objects Astronomy Observatory, which is operated by the Association of Universities appear to have had outbursts that were much more luminous for Research in Astronomy, Inc., under cooperative agreement with the =− National Science Foundation. NOAO proposal 2006A-0046. than that of GK Per (MVmax 9.4), the most luminous CN for 1 The Astronomical Journal, 146:37 (18pp), 2013 August Harrison, Campbell, & Lyke Table 1 Observation Log Name UT Date Start Time Stop Time Instrument DP Leo 2006 Jul 8 05:48 06:18 NIRC DP Leo 2006 Jul 11 03:30 03:46 SQIID EU UMa 2006 Jul 8 06:22 06:56 NIRC EU UMa 2006 Jul 12 03:22 04:57 SQIID V1500 Cyg 2006 Jul 7 11:27 14:06 NIRC (JH) V1500 Cyg 2006 Jul 8 12:10 13:03 NIRC (HK) V1500 Cyg 2006 Jul 12 08:04 11:29 SQIID V2487 Oph 2006 Jul 8 07:21 07:54 NIRC V2487 Oph 2006 Jul 12 04:56 07:51 SQIID HR Lyr 2006 Jul 8 11:46 12:02 NIRC OS And 2006 Jul 8 13:53 14:27 NIRC V373 Sct 2006 Jul 8 09:42 10:33 NIRC V1974 Cyg 2006 Jul 13 05:52 07:36 SQIID V1974 Cyg 2006 Jul 13 09:49 11:45 SQIID V446 Her 2006 Jul 11 04:36 08:47 SQIID V Per 2006 Jul 16 08:59 11:51 SQIID QV Vul 2006 Jul 16 04:11 08:52 SQIID CP Lac 2006 Jul 11 09:02 11:55 SQIID which a high precision parallax has been derived (Harrison et al. 2013a). V1500 Cyg is also unusual in that it is only one of two CNe that have been observed to have a dramatic pre-outburst rise, brightening by 8 mag in the eight months leading up to its eruption (Collazzi et al. 2009). Collazzi et al. also show that V1500 Cyg is one of five CNe (of 22) that have remained much more luminous (∼10×) after outburst, compared to their pre- eruption quiescent levels. This suggests that the accretion rate Figure 1. The near-infrared spectra of four old classical novae obtained with in V1500 Cyg remains much higher than observed for typical NIRC (for clarity, the spectra of HR Lyr and OS And have been offset vertically CNe, and thus, as discussed by Wheeler (2012), such objects by 3.0 × 10−12 and 2 × 10−12 erg s−1 cm−2, respectively). The extraordinarily are excellent progenitor candidates for Type I supernovae. blue continuum of HR Lyr may indicate the presence of cyclotron emission. The question is whether the presence of a strong magnetic field played any role in the unusual outburst (and current) a 256 square InSb array, with a pixel scale of 0.15 pixel−1. properties of V1500 Cyg. Theoretically, it is unclear if strong Besides imaging in the standard near-infrared filters, NIRC had magnetic fields play any role in shaping the outburst of CNe three different grisms providing resolutions of R ∼ 60–120. (Livio et al. 1988; Nikitin et al. 2000), so the only way to know These grisms allowed for the simultaneous observation of two for sure is to identify and characterize more highly magnetic adjoining infrared photometric bandpasses. We observed with CNe. We have obtained both infrared spectra and photometry the GR150 grism and the “JH” filter to obtain spectra covering of V1500 Cyg, and a small set of other old CNe to search for the J- and H-bands, and with the GR120 grism and the “HK” behavior that we can associate with the presence of a magnetic filter to cover the H- and K-bands. Note that simultaneous white dwarf primary. In the next section we describe our spectra covering JHK were not possible, so separate filter/grism observations, in Section 3 we present the infrared spectroscopy moves were necessary with a subsequent set of integrations, to and photometry for the program objects, in Section 4 we discuss obtain such spectra.
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