Photometry and spectroscopy for a bright FeII nova in M81

ATel #1067; A. Rau, S. Gezari, E. O. Ofek (Caltech)
on 4 May 2007; 19:14 UT
Credential Certification: Arne Rau (arne@astro.caltech.edu)

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On April 15 Hornoch et al. reported two apparent novae in M81 (CBET #924). Here we present the results of imaging and spectroscopy follow-up of the 2nd (brighter) event.

Nightly g,r,i' and z' photometry was obtained at the Palomar 60inch Telescope from April 17 to April 27. Exposures were typically 3x180s in each band and the data were photometrically calibrated relative to the SDSS. During the period of observations, the light curve showed a gradual, monochromatic (g-r~0.6 mag, g-i~0.8 mag) decline with a rate of ~0.15 magnitudes per day (see Tables below).

Comparing our photometry to the white light measurements presented in CBET #924, #938, together with r-R~0.2 for g-r=0.6, suggests an observed peak magnitude of the nova of R~18.5. This translates into an absolute peak magnitude of R~-9.4, using a distance modulus of 27.8 (Freedman et al 1994). The decay rate and peak brightness suggest the event to fall in the group of fast novae.

Spectroscopy was obtained on UT April 19.38 (about 5 days after the peak) with the Low-Resolution Spectrograph LRIS on Keck-I. The 400/6000 grism (0.63 angstrom per pixel) and 400/8500 grating (1.86 angstrom per pixel) were used with 900s and 1800s exposure, respectively. We found a blue continuum with broad Balmer emission (Halpha to Hepsilon) with velocity widths of approx. 2000 km/s. In addition strong FeII emission as well as PCyg profiles for NaD and OI were detected. This suggests a spectral classification of type FeIIn, following Williams et. al. (1991, 1994).

Photometry Tables:

## g-band: ##

MJD Mag
---------------------------
54207.367038 19.80+-0.15
54208.189169 20.00+-0.10
54208.312461 19.78+-0.12
54209.223786 19.97+-0.12
54209.386507 20.12+-0.15
54212.330727 20.40+-0.12
54215.198047 20.86+-0.15
54216.195814 20.93+-0.15
54217.184149 20.84+-0.20
54217.350924 21.18+-0.25

## r-band: ##

MJD Mag
---------------------------
54207.379896 19.25+-0.12
54208.201334 19.42+-0.10
54208.353724 19.52+-0.15
54209.231241 19.41+-0.20
54209.395051 19.58+-0.15
54210.274797 19.66+-0.30
54212.338309 20.09+-0.30
54215.210574 20.11+-0.30
54216.205618 20.42+-0.25
54217.191469 20.49+-0.20
54217.358963 20.44+-0.25

## i'-band: ##

MJD Mag
---------------------------
54207.392657 19.08+-0.15
54208.213559 19.19+-0.10
54208.366575 19.11+-0.12
54209.238604 19.25+-0.12
54209.403092 19.18+-0.17
54210.282312 19.53+-0.20
54212.346206 19.81+-0.30
54215.213099 20.02+-0.25
54216.210586 20.38+-0.25
54217.198775 20.33+-0.25
54217.366938 20.70+-0.30

## z'-band: ##

MJD Mag
---------------------------
54208.379577 18.87+-0.20
54209.411474 19.01+-0.25
54215.220448 19.85+-0.30
54216.217938 19.56+-0.20
54217.206071 19.54+-0.20
54217.375010 19.99+-0.25

Lightcurve and Spectrum