J013906.17+524536.89) Photometry Monitoring by Amateur Bruce
Bruce L. Gary, Last Updated 2019.10.16 17 UT
This web site reports photometry measurements of a white dwarf with a suspected planetesimal that is shedding dust debris when its 110-day elliptical orbit brings it close to the star's Roche distance. The presence of fades means that the orbiting debris crosses in front of the star. My intent is to observe this star at intervals of a few days, with all-night observing sessions (in order to assess hourly timescale variations) to record the multi-day "big" fade event Oct 15 ± 2 days and to detect smaller fade events.
J0139 is a white dwarf (DA type, hydrogen atmosphere) that
appears to undergo 30 - 45 % fades at 110-day intervals. Only two
(possibly three) fades have been measured so far. I have adopted
the following tentative ephemeris for the middle of the
fades: JD = 2458661 + E × 110.3. The next two fades are due
on 2019.10.15 and 2020.02.02. The discovery paper, Vanderbosch et
al. (2019), suggests that the fades are due to a planetesimal in a
110-day orbit that is very eccentric (e > 0.97), and during
periastron it is close to the Roche radius of the WD and fragments
are dislodged that form a dust cloud in the same orbit.
List of internal links
Results to date
Physical model suggestion
Observing and Analysis Tips
Results to date
Need someone else's LC to know if this sinusoidal variation is
Still no evidence for target variability during observing session.
Still no evidence for variability during observing session.
Could this be a pulsation?
J0139 is located at RA/DE = 01:39:06.2 +52:45:37.
Figure F1. SDSS image, northeast upper-left.
Figure F3. SDSS image.
Figure F3. Image taken with my AstroTech 16" telescope. FOV = 12.5 x 9.0 'arc, north up, east left.
Figure F4. Some of the stars I use for reference. See below for r'-mags that I've adopted for these stars.
Observing and Analysis Tips for this Target
The target star, J0139, is faint (V = 18.4) so unfiltered is the
best option. However, consider that the target is bluer than all
nearby reference star candidates. The combination of "unfiltered
with very blue target" means that systematic offsets will differ
for each observer (because each observer's unfiltered effective
wavelength will be different). Therefore we should expect that
comparing measurements from different observers will require
determination of an empirical offset for each observer. This is
easy to do. To maximize the usefulness of this process it will be
important that each observer adopt a FOV placement that is the
same every night (so that flat field systematics, which everyone
has, are the same for each observing session). Also, use the same
reference stars every night.
The goal is "day timescale" variations, not hourly or
shorter timescale variations. With a 14" telescope, unfiltered, no
full moon, 100-second exposures will yield SNR per image ~ 10
(i.e., 10 % SE). This SE per image is large compared with all
other systematics. For example, scintillation is typically 5 to 10
mmag per image, or 0.5 to 1.0 %. It is also not necessary to keep
the star field fixed with respect to the pixel field throughout
the night to minimize flat field variations during an observing
The most important tip is to choose photometry setting carefully
and stick to them for processing every observing session.
This is because there's a brighter star close to the target star
(9 "arc away), as shown in the next image. The danger we want to
avoid is for atmospheric seeing changes to cause some of the flux
of the brighter star from entering the signal circle and making
the target star appear brighter than it is. If one observing
session has bad seeing compared to another, there's a risk of the
target reading for that night to be influenced by the nearby star.
My rule of thumb is to choose a signal aperture radius that places
the circle less than halfway to the interfering star.
As an aside, you'll note three "hot pixels" in the above image.
One of them is in the background annulus. This is OK because it
will be ignored (by MaxIm DL, and presumably any other good
quality photometry program). Hot pixels inside the signal circle
cannot be tolerated, so placement of the FOV should take this into
My Collaboration Policy
Please don't ask me to co-author a paper! At my age of 80 I'm entitled to have fun and avoid work. Observing and figuring things out is fun; writing papers is work. If my data is essential to any publication just mention this in the Acknowledgement section.
Vanderbosch, Z., J. J. Hermes, E. Dennihy and 8 others, arXiv: https://arxiv.org/abs/1908.09839
description of J0139
WD1145 photometry monitoring
This site opened 2019.08.30.