[vsnet-alert 22808] Re: ASASSN-18aan

[Tonny Vanmunster tonny.vanmunster@gmail.com via vsnet-alert]

Dear Prof. Nesci,

I read your report with interest and it triggers a question. You mention
that ASASSN-18aan showed a peak at i'=15.4 on 1970.646, with a 1 mag
difference from the previous and following plate, concluding that this was
a flare. What is the timespan between the 1970.646 plate and the "previous"
and "next" one?

I wonder if the 1 mag difference could perhaps be explained through a dwarf
nova (super)outburst instead of a flare? I looked at the ASASSN lightcurve
of ASASSN-18aan, covering a timespan of 2507 days. It shows that the object
is mostly at V= 16.8-17.0 or fainter, with 3 exceptions: it reached V=15.6
on JD 2457189 (2 obs), V=16.3 on JD 2457399 (3 obs) and V=16.0 on JD
2458064 (1 obs). These are all differences of >1 mag compared to
"quiescence".

ASASSN-18aan reached V=15.4 on Nov 30, 2018 and was still at mag g=15.6 on
Nov 2nd. I observed the object last night (Dec 04/05) at CBA Belgium
observatory under moderate skies (clouded out after 2.8 hours), doing
time-series photometry, and found an eclipse of about 0.45 mag in the data,
superimposed on what is most likely a superhump. All this points in the
direction of an eclipsing dwarf nova. The object was at mag 15.6 (CV)
during my observations.

Evidently, further time series photometry will be needed to determine the
exact nature of the object.

So, I'm interested to understand if the 1970.646 observation can be
explained by a 'flare' only, or might have a different origin.

Best regards
Tonny Vanmunster

CBA Belgium Observatorty
CBA Extremadura Observatory
www.cbabelgium.com
www.peranso.com


On Wed, Dec 5, 2018 at 4:44 PM roberto nesci <Roberto.Nesci at iaps.inaf.it>
wrote:

> Roberto Nesci (INAF/IAPS) and Taavi Tuvikene (Tartu Observatory,
> University of
> Tartu, Estonia)report:
> Following the announcement of the transient ASASSN-18aan (vsnet-alert
> 22802) we
> searched in the Asiago archive for plates containing the star. Seventeen
> pairs
> of plates, blue (103aO+GG13) and infrared (IN+RG5) of the 65/90 Schmidt
> telescope containig the star were found, ranging from year 1968 to 1975:
> all the
> plates are of good quality and were digitized with an EPSON 1680 PRO
> scanner for
> an automatic search of Mira variables. The Infrared magnitudes of
> ASASSN-18aan
> were computed with a dedicated pipeline, developed in the frame of the
> APPLAUSE
> project (Tuvikene et al. 2014, ASPL Conf. 127), using as comparison stars
> those
> of the UCAC4 catalog (i' band): details of the photometric procedure are
> given
> in Nesci et al. (2018 RMxAA 54, 341).
> The light curve of the star shows an average value around i'=16.3 and
> shows a
> peak at i'=15.4 on 1970.646, with 1 mag difference from the previous and
> the
> following plate: an eye inspection of the corresponding blue plates
> confirm the
> flare, excluding a plate defect. We are therefore confident to have
> catched an
> historic flare of this star.
> --
> prof. Roberto Nesci,  associated to Istituto Nazionale di Astrofisica,
> (National Institute of Astrophysics) INAF-IAPS, via Fosso del Cavaliere
> 100,
> 00133 Roma, Italia
>
>

-- 
Tonny Vanmunster
CBA Belgium Observatory
CBA Extremadura Observatory
www.cbabelgium.com
www.peranso.com