WHT, DIPOL-2 polarimetry of Nova Sgr 2015b
ATel #7986; Eamonn Harvey (National University of Ireland, Galway) Andrei Berdyugin (University of Turku, Finland), Matt Redman (National University of Ireland, Galway)
on 3 Sep 2015; 11:44 UT
Credential Certification: Matt Redman (firstname.lastname@example.org)
Referred to by ATel #: 8275
We report polarimetry data from three nights observing of Nova Sgr 2015b (also PNV J18365700-2855420 or V5668 Sgr) with the William Herschel Telescope in the BVR passbands using the DIPOL-2 instrument. Spectra of the nova are reported in ATel #7230 #7265, confirming it to be of Fe II type.
The three nights in question are July 4.024, 5.085 and 7.087, after the formation of dust ATel #7643 #7862 and during the local minimum in the transitional part of the optical light curve. The polarimetry data is suggestive of scattering off of small dust grains:
% in B | % in V | % in R
1.6991Â±0.0169 | 0.6008Â±0.0137 | 0.3441Â±0.0072
1.4713Â±0.0152 | 0.5655Â±0.0115 | 0.3300Â±0.0063
1.3375Â±0.0183 | 0.5650Â±0.0231 | 0.3569Â±0.0087
An increase in the position angle of ~4 degrees over the three nights from ~ 144 degrees was observed. The error in the polarization angle was on average 0.3 in B, 0.8 in V and 0.6 in R. There was also a decrease in percentage polarisation in B and V indicative of possible grain and ejecta geometry evolution, R is quite likely dominated by Halpha (private communication Steve Shore).
As the X-ray counts increase over time (ATel #7953) we continue to observe the nova intermittently with 60cm class telescopes and encourage others to do so also, especially in the U band.