Estimate of reddening for T Pyx based on optical diffuse interstellar bands (DIBs)
ATel #3306; S. N. Shore (Pisa), T. Augusteijn (NOT), A. Ederoclite (IAC), H. Uthas (Columbia University)
on 26 Apr 2011; 03:48 UT
Distributed as an Instant Email Notice Novae
Credential Certification: S. N. Shore (shore@df.unipi.it)
We report the first results for the latest outburst of the recurrent
nova T Pyx from the FIES echelle spectrograph on the 2.6 m Nordic
Optical Telescope (NOT) at La Palma from 3700-7200 A with a resolution
of 67000. The first spectrum, obtained on 2011 Apr. 15.92 UT during the
rise to maximum (V \approx 9.5) with integration time of 600 sec with
a S/N of 30 at 6000 A (continuum), was sufficiently well exposed to
display some of the strongest optical diffuse interstellar bands
(DIBs). Friedman, S. D. et al. (2011, ApJ, 727, 33) provide
calibrations of the neutral and molecular hydrogen column densities
and reddening E(B-V) for 5870, 6205, 6283, 6405, 6614, uncertainties
in the measurements are +/- 3 mA with a systematic (calibration)
uncertainty of about 10% for each DIB. Our mean reddening is
E(B-V)=0.44+/-0.18 with all values being greater than 0.2. The two
strongest DIBs, 5780 A and 6283 A, agree in mean velocity with the
mean radial velocity of the Na I D and Ca II H and K lines measured on
the same spectra, both ions showing components at +26 and +35
km/s. The velocities agree with a spur noted in the H I 21 cm
line measurements in the 4th quadrant. The DIB 6204 A appears, instead,
to have a velocity of around +15 km/s. There are no archival STIS or
GHRS spectra of sufficiently high velocity resolution along this line
of sight with which these can be compared (unlike e.g. V407 Cyg (Shore
et al. 2011, A&A, 527, A98; also obtained with FIES and which which
our present spectra were compared for identification). The higher
positive velocity Na I D component is marginally saturated, with FWHM
of 7 km/s while the weaker, lower velocity component is broader, 14
km/s. A second spectrum, also a 600 sec expoure, obtained on
Apr. 23.92 UT confirms the presence of the features and their
equivalent widths. This reddening value is higher than both the Schlegel,
Finkbeiner, & Davis (1998, ApJ, 500, 525) value in this direction and
the value, ~0.25, based on the colors of the system and the previous
outbursts and may affect planning for optical and ultraviolet
satellite observations and for interpreting XR data.
