Significant colour change of ASASSN-15ni observed with the UCD Watcher telescope
ATel #7875; A. Martin-Carrillo (University College Dublin, UCD), D. Murphy (UCD), L. Hanlon (UCD), M. Topinka (CTU), H. J. van Heerden (UFS), B. van Soelen (UFS) and P. J. Meintjes (UFS)
on 5 Aug 2015; 23:07 UT
Credential Certification: Antonio Martin-Carrillo (antonio.martin-carrillo@ucd.ie)
Subjects: Optical, Cataclysmic Variable
We continue to monitor the cataclysmic variable ASASSN-15ni (ATel #7850) with the 0.4m UCD Watcher robotic telescope at Boyden Observatory (South Africa). Observations are carried out using 3 filters (SDSS g', r' and i') with exposure times ranging from 10 to 30 seconds.
In our first set of observations from July 28 (ATel #7855), ASASSN-15ni appeared as a blue source with a colour index of r' - g' = 0.14 +/- 0.04 and i' - g' = 0.35 +/- 0.04, consistent with ATels #7854 and #7859. Using data obtained for 9 nights from July 28th to August 5, we observe that the brightness of the source was decaying as a power-law until August 4. No significant change in brightness is seen between August 4 and August 5 suggesting a possible flattening. No significant variability is seen in any filter at short timescales.
The current average magnitudes obtained on August 5 (18:21 - 19:21 UT) are r' = 14.39 +/- 0.04, i' = 14.41 +/- 0.07, g' = 14.44 +/- 0.02. These new magnitudes suggest a spectral change where the source is significantly redder than on July 28, with colour indices of r' - g' = -0.05 +/- 0.05 and i' - g' = -0.03 +/- 0.07.
We plan to continue observing ASASSN-15ni.
