Near-infrared observations of Nova Sco 2015 and the luminous red variable in M31
ATel #7236; M. Srivastava, N. M. Ashok, D. P.K. Banerjee, V. Venkataraman; Physical Research Laboratory, Ahmedabad, India
on 17 Mar 2015; 09:33 UT
Credential Certification: Dipankar P.K. Banerjee (orion@prl.res.in)
Subjects: Infra-Red, Nova, Transient
Near infrared observations are reported of Nova Sco 2015 (PNV J17032620-3504140) and the luminous red variable in
M31 (Nova M31N 2015-01a = MASTER J004207.99+405501.1 )
using the Mount Abu 1.2m telescope and the 1024x1024 HgCdTe NIR camera/spectrograph (NICS).
Spectra Of Nova Sco 2015 (0.85 to 2.4 microns, R = 600 - 1000) were obtained on 8 epochs between
18 Feb 2015 to 8 March 2015. The FWHM of the H emission lines, as measured from the Paschen beta and
Brackett gamma features,
show
a significant narrowing with time reducing from an FWHM of 1700-1800 km/s on 18 Feb 2015 to 500-600 km/s on
8 March 2015 (FWHM's are not deconvolved for instrumental broadening). Similar behavior has earlier been
observed in RS Oph, V407 Cyg, V745 Sco and Nova Sco 2014
indicating a decelerating shock as the nova ejecta collides and is slowed down by the wind of a giant companion.
Nova Sco 2015 thus appears to be part of a symbiotic system (ATel #7060).
The NIR evidence for hot shocked gas is consistent with the findings of
a hard X-ray flux and non-thermal synchrotron radiation from the source (ATels #7085, #7194 ).
JHK photometry of the luminous red variable in M31 ( ATels # 6911, #6985, #7150, #7173, #7208) was obtained on 6 March 2015.
The source has been identified as a likely stellar merger (or "luminous red nova") of the V838 Mon type. We obtain J = 14.05, H = 13.40 and K = 13.0 (typical error +-0.05). The NIR magnitudes, corrected for extinction using Av = 0.77 (i.e Aj = 0.2, Ak = 0.07; Schlafly and Finkbeiner 2011), likely indicates a K giant spectral type for the source
( also see ATel #7208). No IR excess is seen indicating that dust formation has yet to commence in spite of the consistent shift of the optical colors towards the
red in recent times (ATel #7150).
