[vsnet-alert 23353] ASASSN-19lw outburst

Fri Jul 5 22:06:56 JST 2019

During the first snapshot of Gaia17amf object in Lupus with iTelescope
T32 in Siding Spring I have caught the outburst of the poorly studied
dwarf nova ASASSN-19lw originally discovered by ASAS-SN on 2019 May
03.97 at 16.1g. Checking the current ASAS-SN light curve (Shappee et
al., 2014; Kochanek et al., 2017) confirms the on-going outburst:

https://asas-sn.osu.edu/light_curves/1d399fcf-9eab-4489-8399-d6781bef4ead

ASASSN-19lw
  20190702.9167  >169g   ASAS-SN last non-detection
  20190704.9029  15.96g  ASAS-SN Outburst!
  20190704.9041  16.05g  ASAS-SN
  20190704.9053  15.93g  ASAS-SN
  20190705.0905  15.94g  ASAS-SN
  20190705.0918  16.06g  ASAS-SN
  20190705.0931  15.80g  ASAS-SN
  20190705.3641  15.79CV T32

The rise and fall of discovery outburst in May was too slow for UGSU
or UGSS dwarf nova. Overall light curve reminds more of a UGZ-type
variable with sawtooth-shaped peaks starting since 2018 Sep. 08-10.
Yet there were no outbursts detected in Feb. 2016 - Aug. 2018. It
looks like there was a standstill then.

However, ASAS-SN upper limits are varying by nearly 2 mag with the
lunar cycle, thus the unluckily timed outbursts with the cycle length
close to 1 or 2 months can be systematically missed. Follow up CCD
observations are needed to establish the type and cycle of this
variable.

While observing this dwarf nova, please keep an eye at a very
interesting object Gaia17amf which is 10' West and 1' North of
ASASSN-19lw. It was not detected by Gaia in 14 epochs during 2014-2016
to m_lim=21.5, then it has turned on showing irregular outbursts up to
16.8m, being brighter than 21.0m on 11 of 15 epochs in 2017-2019. See
[vsnet-alert 20703] and the Gaia light curve at
http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia17amf/ for details.

Color-combined DSS finder chart centered right in between of
ASASSN-19lw and Gaia17amf is posted at
http://scan.sai.msu.ru/~denis/ASASSN-19lw-Gaia17amf.jpg (15'x10' FOV,
North up, East left).

VSX entries for both objects:
https://www.aavso.org/vsx/index.php?view=detail.top&oid=687609 - ASASSN-19lw
https://www.aavso.org/vsx/index.php?view=detail.top&oid=477071 - Gaia17amf

Denis Denisenko