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UKIDSS archival measurement of ASASSN-15qd

ATel #8136; Thomas J Maccarone (Texas Tech University)
on 7 Oct 2015; 01:05 UT
Credential Certification: Tom Maccarone (thomas.maccarone@ttu.edu)

Subjects: Infra-Red, Optical, Nova

Referred to by ATel #: 8150

ATEL #8126 reports ASASSN15-qd, a new candidate classical nova in the Galactic Plane. We have searched the UKIDSS Galactic Plane Survey database and have found that there is an object at this position with K=17.1+-0.1 found in the survey. The source is UGPS J192150.15+150924.8 (Lucas et al. 2008, MNRAS, 391, 136). ATEL #8126 reports a likely distance range of 2-15 kpc. Typical classical novae have absolute magnitudes at peak of about M_V=-8, so we take the low end of the range, where the ASASSN15-qd would be at M_V=-8.3 as most likely. ATEL #8126 reports an extinction estimate of 11.5 magnitudes in V, which leads to A_K of 1.3 magnitudes. We thus estimate that the K-band absolute magnitude of the pre-cursor to the nova candidate is M_K=4.3. For typical colors of a bright cataclysmic variable, this is likely M_V = 3.8 or so, easily faint enough to have been undetected in pre-outburst optical data. Typically, novae are expected to occur in nova-like cataclysmic variable stars, which have high accretion rates. Novalike systems are typically found at absolute magnitudes similar to those of dwarf novae in outbursts at the same orbital period, and in turn, follow the Warner (1987, MNRAS, 227, 23) relation: M_V = 5.6 -0.26 P_orb(hr) This would then correspond to a 7 hour orbital period, a value at which one expects to see high accretion rate cataclysmic variables. The numbers are quite approximate, stemming from the uncertainty due to original assumption in ATEL #8126 of a nova color of 0.0 to estimate the reddening (an assumption which is quite reasonable, but not yet well established). Regardless,the interpretation of the event as a classical nova is bolstered by finding an infrared counterpart with reasonable properties for such a scenario.