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Alert Notice 680: Monitoring of J0139 (ZTF J013906.17+524536.89) requested - corrected

Note: This Alert Notice has been edited to correct the mis-spelling of the short form of the star name. It is J0139, not J1039.  -  E. O. Waagen, September 18, 2019

September 18, 2019

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
 - Campaigns and Observing Reports
: https://www.aavso.org/j0139-campaign

AAVSO member and observer Bruce L. Gary (Hereford, AZ) is requesting daily monitoring of the faint eclipsing (E+ZZA) white dwarf J0139 (ZTF J013906.17+524536.89).

He writes: "I don't have more info than what is in the public domain. However, this star system has the potential to be scientifically important since it is only the second WD exhibiting transiting dust clouds (WD1145 being the first). Since 97% of stars end up as WDs, and 1/3 of WDs show evidence for in-falling dust from disintegrating planetesimals (i.e., polluted atmospheres), this category of star system has broad implications, especially for our solar system's future.

"We can't be sure that J0139 has repeating dips (at 110-day intervals) because only two dips of similar depth and shape have been observed, and one very brief dip at the expected time is weak corroboration. It's possible that the broad dips (several day duration) will not happen again in the near future, centered on 2019 Oct 15 and 2020 Feb 02, given that the last observed dip was very brief. However, due to the potential scientific value of this system I would like to see the advanced AAVSO CCD observers provide daily monitoring of J0139.

"The evidence so far is that dust clouds pass in front of the star such that brightness variations have a timescale of a few days, so nightly observations should be sufficient. However, because of the star's faintness (r'-mag = 18.41), and the low SNR for reasonable exposure times (e.g., SNR = 10 for 60-second exposures), an observing session should be at least an hour long when using telescopes with an aperture of < 20". Unfiltered observations are recommended. [J0139 has a range of 18.45-19.0 g.]

"October 10 to 20 will be the most important dates for observing since Oct 15 is when the next major dip of 30 to 45% depth is predicted. Smaller dips of 5 to 10% are probable at other times." VSX has an ephemeris of additional predicted dips. For these dips, coverage is recommended for the ten days centered on each predicted dip.

Two relevant links for J0139 provided by Gary are: wikipedia and BGary.

Please note that this object has been added to the AAVSO Target Tool as J0139.

Coordinates (J 2000.0): R.A. 01 39 06.17  Dec. +52 45 36.9

Charts: Charts with comparison stars for J0139 may be created using the AAVSO Variable Star Plotter (VSP). When creating a chart, choose F (18.5 arcmin) or G (7.5 arcmin) scale to see faint enough comparison stars.

Submit observations: Please submit observations to the AAVSO International Database using the name J0139 or ZTF J013906.17+524536.89.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.
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