Amateur Photometric Monitoring of Croll's List of While Dwarfs with Polluted Atmospheres
B. L. Gary, Last updated 2015.12.12 UT

This web page is a "jumping off" place for amateurs who have been invited to monitor a selection of white dwarfs with polluted atmospheres. The supervising professional astronomer is Dr. Bryce Croll, of Boston University, who has provided a list of polluted WDs for observation. Dr. Saul Rappaport is supporting this project with modeling. The goal is to search for evidence of transit fades produced by dust clouds associated with an asteroid that is disintegrating. The most recent inspiration for this task is a pair of papers Vanderburg et al (2105), using Kepler K2 data, and Croll et al (2015), using ground-based data, describing the dusty WD 1145+017 that shows unusual transit features. This WD's transits at intervals of 4.5 to 4.9 days has been convincingly shown to be produced by dust clouds associated with asteroids in orbits with periods in the same 4.5 to 4.9-day interval. Since the dust clouds are much larger than the asteroid the transit length is ~ 5 to 10 minutes, which is much longer than the length that would be produced by just the asteroid's transit (~ 1 minute). Depth can be as large as 60% (i.e., ~1.0 mag, flux ratio = 0.40). One goal for the present observations is to establish a transit ephemeris (and such characteristics as depth, length and reliability of transit features) prior to the professional telescope observing campaign scheduled for February and March, 2016. Another goal is to determine if any of the other WDs exhibit transits. 

 Here's the current list of WDs known to be dusty (having polluted atmospheres) that are high priority for observing.


List of WD targets provided by Dr. Bryce Croll.

These observations will be conducted by advanced amateurs using telescope apertures of 11" to 14" typically. The team of observers who have accepted our invitation is given below. After an observing session the observer is asked to attach a LC to an e-mail to me so that I can place it on a web page devoted to the WD that was observed. Links to each WD are given below. I will maintain a summary of results on this web page.

Links on this web page
    Summary of results
    Links to each WD
    Observing team, suggested observing procedure & msc comments
    References
    Related external links 

Summary of Results to Date

1) G28-39 has large pulsations (~ 0.2 mag) with 4 LS components with periods between 6 & 14 minutes.

2) WD 1145+017 has exhibited a pattern of 4 fades that repeated 22 hours apart (5 rotation), suggesting an orbital period of 4.495 hours. On Nov 21 a total of 7 fade events were seen during a 3.0-hour observing session. Overlapping LCs for two dates show essentially identical patterns of fade events. Depths are larger than previously published, being as much as ~ 1.0 mag.

Links to Each WD & Hours of Observations 
    1  PG 0843+516 0843+516   22.5
    2  PG 1015+161 1015+161  
    3  WD 1145+017 1145+017  ???.?
    4  WD 1226+110 1226+110  
    5  NLTT 43806  1653+385   1.6 = 1.6   
    6  WD 1929+012 1929+012   3.2 = 3.2
    7  G29-38      2326+049  23.6 = 7.8,4.9,4.2,4.9,1.8

Observing Team, Suggested Observing Procedure & Miscellaneous Comments   

Contributing Team Members

    Bruce Gary               14"             Arizona               Currently the most active observer
    Jerry Foote               16"             Utah                     Active observer
    Tom Kaye                32"             Arizona               Will observe WD 1145+017 with 32"; some remote control issues have to be dealt with first
    Paul Benni               11"             Massachusetts     Needs good weather

Expressed Interest But No Submissions Yet

    Roberto Zambelli    11" & 16"    Italy                    Will participate when a CCD is repaired
    Joe Garlitz               12"              Oregon                Joined Kilic team so status unknown

I suggest observing unfiltered with exposure times of 30 to 60 seconds (depending on telescope aperture). Try to use the same reference stars (ensemble photometry) and APASS magnitudes (r'-band will probably most resemble unfiltered). A good place to get APASS mag's is from the UCAC4 catalog (using C2A).

WD 1145+017 is a high priority target that we want to observe before professional observations begin in February. We want to catch a few transits for establishing a new transit ephemeris and depth behavior to help in scheduling large telescope observations.


References
    Vanderburg et al (2015) arXiv (Nature, 2015 Oct 22).
    Croll et al (2105) arXiv 
    HuffPost article about J1228+1040 (with disintegrating asteroid dust ring)

Related Links  
    Dr. Bryce Croll web page
    Some observing "good practices" for amateurs (book): Exoplanet Observing for Amateurs
    Master list of my web pages & Resume

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WebMaster: B. Gary.  Nothing on this web page is copyrighted. This site opened:  Nov 01, 2015