6. White Dwarf WD 1145+017 Photometric Monitoring Observations by Amateur Observers B. Gary & T. Kaye
B. L. Gary, this is the 6th of 6 web pages. Last updated 2019.03.234 04 UT

1 of 6 - 2015.11.01 to 2016.01.21:  LC Observations  - 1st  set of LCs, for 2015/16 observing season   
2 of 6 - 2016.01.17 to 2016.07.13:  LC Observations  - 2nd set of LCs, for 2015/16 observing season    
3 of 6 - 2015.11.01 to 2016.07.13:  LC Observations  - 3rd set of LCs, for 2015/16 observing season  (N = 158) + Overview, Results & Model Speculations 
4 of 6 - 2016.10.25 to 2017.06.18:  LC Observations  - 4th set of LCs, for 2016/17 observing season 
5 of 6 - 2017.10.23 to 2018.06.18:  LC Observations  - 5th set of LCs, for 2017/18 observing season 
6 of 6 - 2018.11.06 to now              LC Observations  - 6th set of LCs, for 2018/19 observing season   (YOU ARE HERE)

Links on this web page:

  Status & Summary of Results for this Observing Season  
  Observing session LCs 
  Finder image & basic info  
  Miscellaneous analysis and speculation  
  Data exchange files (for all years: 2015/16, 2016/17, etc)
  My collaboration policy 
  References & related external links 

Status & Summary of Results for this Observing Season: 

W
e now have ground-based observations for dips associated with the A, B and D asteroids (i.e., from 2015 to 2019). On 2019.02.12 a D dip was observed twice during one observing session; this LC is used to create an accurate D ephemeris for use with a waterfall plot for monitoring D dip activity. Several D dips were later observed with waterfall drift lines that converge backward in time to a "creation date" of 2019.02.19. At this time just one dip is present. On 2019.03.01 T.Kaye and I observed a very short duration dip (113 seconds, apparent FWHM), which was broader 3 days later.



Full moon 34 degrees away, so noisy.















Figure 2a.
"Activity level" for past 4 years.


Figure 2b. "Activity level" for the past 1.5 years.


Figure 2c. "Activity level" for the present observing season.
 

Figure 3a.  Drift line plot for seasons 2017/18 and some of 2018/19. The red lines have the same ephemeris (period and BJDo).


Figure 3b.  Drift line plot for the present observing season. (I don't believe all of the dotted lines either!) DOY 390 corresponds to 2019.01.25, when it appears that the dust cloud associated with the red drift line generated two additional fragments that became active in producing dust clouds. The steeply sloped green drift line has the D asteroid ephemeris period (4.5500 hours).   


Figure 4. D-fragment ephemeris, showing at least one dip "belonging" to this ephemeris (at phase 0.50). Perhaps 6 other dips also belong to the D-fragment period.  

List of observing sessions   

2019.03.23 - BG
2019.03.15 - TK32 
2019.03.15 - TK16 
2019.03.15 - BG  
2019.03.14 - BG 
2019.03.09 - TK 
2019.03.09 - BG 
2019.03.04 - TK 
2019.03.04 - BG
2019.03.01 - TK 
2019.03.01 - BG 
2019.02.28 - BG 
2016.02.26 - TK  
2019.02.26 - BG  
2019.02.25 - TK 
2019.02.24 - TK 
2019.02.24 - BG 
2019.02.23 - BG  
2019.02.18 - TK 
2019.02.18 - BG 
2019.02.17 - TK 
2019.02.17 - BG 
2019.02.16 - BG 
2019.02.12 - TK 
2019.02.12 - BG 
2019.02.07 - TK 
2019.02.07 - BG
2019.02.02 - TK
2019.01.28 - TK 
2019.01.27 - TK
2019.01.27 - BG
2019.01.20 - TK
2019.01.19 - TK
2019.01.19 - BG 
2019.01.17 - TK 
2019.01.15 - TK
2019.01.15 - BG 
2019.01.12 - TK
2019.01.12 - BG  
2019.01.04 - BG 
2018.12.19 - BG 
2018.12.10 - BG  
2018.12.09 - BG  
2018.12.04 - BG   
2018.11.27 - BG    
2018.11.16 - BG
2018.11.09 - BG  

Observing Sessions  


2019.03.23 - BG

Full moon was ~ 34 deg away, causing high noise level.







219.03.15 - TK32


This is an average of data from 3 telescopes.


 


219.03.15 - TG16 


After averaging in groups of 3.





2019.03.15 - BG  







2019.03.14 - BG  







2019.03.09 - TK 







2019.03.09. - BG 







2019.03.04 - TK 


Averaging groups of 5 (after sorting all observations of this date by phase).


Averaging groups of 3 (after sorting all observations of this date by phase).


No averagin (a symbol for each image). Both data sets show a brightening at phase 0.11. Could this be forward scattering from a dust cloud that doesn't block the WD disk?





2019.03.04 - BG 





2019.03.01 - TK 







2019.03.01 - BG







2019.02.28 - BG 


Dip #1 has changed shape since the day before: ingress is brief and egress is slow. One of the group of 3 D dips has disappeared (the middle one). Of these 6 dips 3 are produced by A fragment and 3 are produced by D fragments.





2019.02.26 - TK  











2019.02.26 - BG  







2019.02.25 - TK 







2019.02.24 - TK 









2019.02.24 - BG 





2019.02.23 - BG


I'm not saying the dip at phase 0.56 is the D dip, first seen on Feb 12, because it may just be a coincidence that it is located where we were looking for it. 


A gibbous moon (81 % illuminated) was 30 degrees away, which decreased SNR significantly. The first and last dips are 4.55 hours apart.

2019.02.18 - TK 




A cleaned-up version.

2019.02.18 - BG 



2019.02.17 - TK 





2019.02.17 - BG 





2019.02.16 - BG 

I was "desperate" to observe that D dip, but cloudiness ruined my observations.





2019.02.12 - TK 


Using the Kepler D period = 4.5500 hrs (and an arbitrary BJD_ref) this date's phase-folded LC for both HAO and TK16 data, shows the D dip stable in phase, at 0.79.



2019.02.12 - BG 

On this date a "sharp" dip was first seen that belongs to the D-fragment orbit. During one LC the dip appeare twice, with a separation o 4.552 +/- 0.004 hours.


This analysis shows that with an exposure time of 60 seconds, and a cadence of 71 seconds, the actual dip depth (assuming it's the same for the first and second appearance) is slightly deeper than the solution based on measurements. A source function with a deeper depth was convolved with a rectangular exposure function at appropriate exposure start times, and these results are shown by the red dash symbols. The source function has a depth of 25 % (vs. the 23 % that fits the measurements). There is negligible affect on the apparent width of the dip caused by a finite exposure time.


This is the AHS model fit when the measured values are fitted (using sum chi-squares), using one depth and shape with a UT offset for the second appearance of the dip following the first appearance by 4.552 hours (also solved-for). 

 
Using the Kepler D period = 4.5500 hrs (and an arbitrary BJD_ref) this date's phase-folded LC for HAO data shows the D dip stable in phase, at 0.79. (I later refined the D dips period to be 4.552 hrs.)


Phase folding with the A-fragment period shows the main dips at different phases.


The more accurate separation of the two main dips is 4.552 +/- 0.004 hours.


This is the LC that forced me to recognize that a D dip was present, and it was "sharp" (like most dips at "turn-on").

2019.02.07 - TK  





2019.02.07 - BG 





2019.02.02 - TK 





2019.01.28 - TK 





2019.01.27 - TK





2019.01.27 - BG





2019.01.20 - TK 





2019.01.19 - TK 





2019.01.19 - BG 



2019.01.17 - TK 




This was a short test observation meant for checking master calibration files, but it's somewhat useful for excluding presence of dips.

2019.01.15 - TK 




We are puzzled about the main dip being shallower in this (TK) data than BG data.

2019.01.15 - BG 


Note: There is no evidence of the "double-dip" feature that was present on Jan 12.

2019.01.12 - TK 




First observations with TK's new 15" telescope. No calibration (dark or flat).

2019.01.12 - BG  


Dew formed on my front corrector plate, starting (probably) ~ 9 UT.

2019.01.04  





2018.12.19 





2018.12.13





2018.12.10  




This dip is credible.

2018.12.09 


I'm skeptical about the two dips at the beginning.

2018.12.04



2018.11.27


 

2018.11.16



2018.11.09 


This is the first observation of the season.


Finder Image and Basic Info

RA/DE = 11:48:33.6, +01:28:29. Observing season centered on March 16
V-mag = 17.2, B-V = -0.08 +/- 0.04, spectral type = DBAZ
Distance from Earth = 142 parsecs
(Izquierdo et al., 2018)
WD mass = 0.63 0.05 x Earth mass
= 1.19e30 kg (Izquierdo et al., 2018)
WD radius = 1.32
0.07 x Earth = 8419 km (Izquierdo et al., 2018)
WD Teff = 15,020
520 K (Izquierdo et al., 2018)
A asteroid radius and mass = ~ 200 km and 1/10 Ceres, i.e., ~ 1020 kg (Rappaport et al., 2016)
Kepler-based transit periodicities (A - F) = 4.49 to 4.86 hours, (Vanderburg et al., 2015)
Asteroid orbital speed (A - F) = 319 to 311 km/s
A asteroid time to cross WD diameter = 53 seconds (for central crossing)
A asteroid transit depth ~ 0.56 mmag (assuming 200 km radius)


WD1145 (blue circle) is at 11:48:33.59 +01:28:59.3 (J2000). Red-circled stars have stability suitable for use as reference. FOV = 27 x 18 'arc, northeast at upper left.

Miscellaneous Analyses and Speculations

So far ground-based observations have detected dust clouds with orbits associated with the K2 measurements of the A, D and B periods, as shown below. 


Figure M01. Scatter plot for some of the drift lins of the past few years, converted to average orbit radius. 



Figure M02. Same data for just the inner-most three orbits. The WD radius ~ 8400 km, so the A dust clouds are typically ~ 700 km closer to the WD than their parent asteroid.

The above two graphs are based on plots like the following:


Figure M03. Waterfall plot for the 2017/18 observing season, using the A ephemeris (as described in Rappaport, 2018).


Figure M04. Waterfall plot for the current observing season, using the A ephemeris (as described in Rappaport, 2018).


Figure M05. Waterfall plot for the current observing season, using the D ephemeris (described below)

This waterfall plot has evidence for the creation of several fragments of the D asteroid on DOY 416 (2019 Feb 19).

The use of P = 4.552 hours is required by the 2019 Feb 12 light curve, below.


Figure M06. This standard light curve shows two "sharp" dips with identical shapes that are separated by 4.552 +/- 0.004 hours, which corresponds to the K2 D period (4.550 hours).



Figure M07. Detail of the first and second appearance of a dip with identical structure on 2019 Feb 12 (shown in previous figure) separated by 4.552 +/- 0.004 hours. The times of image exposures is shown by the x-location of the red bars, and the average of a hypothetical source function normalized flux during these exposure times is shown by the red bar y-locations. The source function was adjusted to achieve agreement with the observations. 

This detail of the two dips shows that the 60-sec exposure times had only a slight effect on inferred depth of the "source function" (what would have been observed with short exposures). The source function has a depth of 25 %. How can a dust cloud that covers 25 % of the WD disk cross in only 2.5 minutes, considering that a point source crosses the disk in only 0.9 minutes? This deserves an analysis of the geometry of cloud size and crossing time.

Speculation:

Let's tell a story describing what may have happened in the D orbit last week.


Figure M08. Distance where Roche lobe surface has shrunk to coincide with the asteroid's surface as the asteroid orbit shrinks, vs. distance from WD1145, for a suite of asteroid densities.

The gravitational field at a distance of ~ 100 x WD radius is strong enough to synchronize an asteroid's rotation with its orbital motion. The surface of the Hill sphere (Roche sphere) is where WD and asteroid D have equal gravity (in a rotating coordinate system), and it will be approximately coincident with the D asteroid's surface if the asteroid's density is ~ 3.2 [gm/cm^3], as shown in the above graph.

If the D asteroid has a density of ~ 3.2
[gm/cm^3] it will be at risk of losing dust and fragments on its surface when the smallest of ejection velocity outward is imparted to the dust or fragment. In other words, there is no "escape velocity" for such an asteroid, and the smallest nudge will send surface material "floating" away from the asteroid. This suggestion was made by Rappaport (2016) as a means for producing a population of fragments in orbits interior to the asteroid. The reason only interior orbits will be populated is that fragments will more likely be ejected from the hot pole, the end of the asteroid facing the WD, than from any other surface location. (Note: the WD gravity field radial gradients are so great at 100 WD radii that any asteroids at this distance will be rotating synchronously with their orbital period.) The reason for regarding the hot pole as the only source for fragments is related to the fact that the hot pole will have a heat wave penetrating the asteroid surface starting with a surface temperature of ~ 1400 K, whereas the asteroid sides and opposite pole will be much colder. When the heat wave encounters a layer with volatile minerals the sublimation of solid to gas can create a cavity with pressurized gas that will eventually overcome the structural strength of overlying material and eject the that material outward.

After this outward ejection of material, or fragment, a fresh surface is exposed at two places: on the asteroid and one side of the fragment. Both will initially be colder than the 1700 K steady-state surface temperature, but they will begin to heat and produce a "heat wave" that penetrates underlying material. After the surface of each body reaches 1700 K they may "turn on" the sublimation process at some level where the most volatile mineral resides. The timing of when fragment dust clouds are produced should depend on the rotation state of the fragment. If it rotates fast the the steady-state surface temperature will be lower than if it isn't rotating. Assuming the fragment achieves synchronous rotation it will become hotter on the star-facing end, and this is where dust production should occur. There are several factors that can influence activity fragment level, such as the time to achieve synchronous rotation, but also fragment shape. It is well known that the bottom of moon craters are hotter than flat surfaces, due to crater bottoms having a smaller than hemisphere for radiating away heat. The same thing can exist on the asteroid and its fragments. I have estimated that 1900 K is possible, using the moon example. Crater bottoms may therefore be favored locations for the ejection of dust, or additional fragments.

Here's a repeat of the waterfall plot using the D ephemeris that was established by the two dips analyzed in the previous two figures.


Repeat of Fig. M05.

In the above figure let's imagine that the D asteroid has a large crater that has reached a surface temperature of ~ 1900 K. Near surface sublimation occurred and produced a small dust cloud at DOY 408. Since its source is the asteroid it will have a center of activity fixed to the asteroid period, not a period associated with an orbit at the asteroid's front surface. The asteroid's front surface may be 100 km closer to the WD than the asteroid center, This is indicated by the first vertical green bar.

This activity subsided by DOY 413, shich accounts for a gap between the vertical green bars. A subsurface heat wave reaches lower levels that exceed the temperature of a layer with volatile mineral, causing the formation of a gas chamber with pressures that eventually exceed the strength of overlying material. An explosive ejection of four fragments occurs on DOY 416. Since it was a crater on the star-facing surface that was the source of the explosive ejection the ejected fragments will be in elliptic orbits with a smaller average orbit radius than the parent asteroid. None of the ejection velocity is lost by overcoming the asteroid's gravity because the WD gravity field matches the asteroid's gravity (in a rotating reference frame). This is equivalent to stating that the Hill sphere radius (same as Roche lobe) equals the asteroid radius. In theory, a rock on the surface could "float away" with the smallest nudge.

After 4 or 5 days these fragments became active sublimators on their fresh surfaces, producing the 3 or 4 drift lines sloping off to the left.

... [more to come] ...


Data Exchange Files   

    2015.11.21 to 2016.01.20  
    2016.11.
    2017.11.
    2018.11.09 to 2019.03.15  


My Collaboration Policy

Please don't ask me to co-author a paper! At my age of almost 80 I'm entitled to have fun and avoid work. Observing and figuring things out is fun. Writing papers is work. Besides, most people really don't care about what others have done. (Google "WD 1145+017" and among the several pages of lame links none point to my web pages.)

My light curve observations will be "in the public domain" for this observing season (2017/18). This includes a download of all LC observations, which I invite anyone to use. If my data is essential to any publication just mention this in the acknowledgement section (no co-authorship, please).

Data Exchange Files

Data exchange files are available in two formats: light curve details (normalized flux for each image) and dip statistics (asymmetric hypersecant model fits for each dip). The first of these is available for download here, but I recommend that anyone using these data check with me for updates (since I sometimes find errors and post the corrected files here). Data exchange files of the second format (dip stat's) will be available here in due time.

 

References


    Vanderburg, Andrew and Saul A. Rappaport, 2018, "Transiting Disintegrating Debris around WD 1145+017," arXiv 
    Rappaport, S. B. L. Gary, A. Vanderburg, S. Xu, D. Pooley & K. Mukai, "WD 1145+017: Optical Activity During 2016-2017 and Limits on the X-Ray Flux," MNRAS, arXiv 
    Xu, S., S. Rappaport, R. van Lieshout & 35 others, "A dearth of small particles in the transiting material around the white dwarf WD 1145+017," MNRAS link, preprint arXiv: 1711.06960 
    Vanderburg et al, 2015, "A Disintegrating Minor Planet Transiting a White Dwarf," Nature, 2015 Oct 22, arXiv:1510.063387
    Croll et al, 2105, "Multiwavelength Transit Observations of the Candidate Disintegrating Planetesimal Orbiting WD 1145+017," ApJ, arXiv:1510.06434 
    Gaensicke et al, 2015, "High-Speed Photometry of the Disintegrating Planetesimal at WD 1145+017: Evidence for Rapid Dynamical Evolution," arXiv :1512.09150
    Rappaport, S., B. L. Gary, T. Kaye, A. Vanderburg, B. Croll, P. Benni & J. Foote, 2016, "Drifting Asteroid Fragments Around WD 1145+017," MNRAS, arXiv:1602.00740
    Alonso, R., S. Rappaport, H. J. Deeg and E. Palle, 2016, "Gray Transits of WD 1145+017 Over the Visible Band," Astron. & Astrophys., arXiv:1603.08823
    Petit, J.-M and M. Henon, 1986, Icarus, 66, 536-555 (link)
    Veras, Dimitri, Philip J. Carter, Zoe M. Leinhardt and Boris T. Gansicke, 2016, arXiv 
    Gary, B. L., S. Rappaport, T. G. Kaye, R. Alonso and F.-J. Hamsch, "WD 1145+017 Photometric Observations During Eight Months of High Activity," 2017, MNRAS, 465, 3267-3280. PDF  or arXiv  
    Hallakoun, N., S. Xu, D. Maoz, T.R. Marsh, V. D. Ivanov, V. S. Dhillon, M. C. P. Bours, S. G. Parsons, P. Kerry, S. Sharma, K. Su, S. Rengaswamy, P. Pravec, P. Kusnirak, H. Kucakova, J. D. Armstrong, C. Arnold, N. Gerard, L. Vanzi, 2017, Earth and Planetary Astrophysics, arXiv 1702.05486
    Farihi, J., L. Fossati, P. J. Wheatley, B. D. Metzger, J. Mauerhan, S. Bachman, B. T. Gansicke, S. Redfield, P. W. Cauley, O. Kochukhov, N. Achilleos & N. Stone, "Magnetism, X-ras, and Accretion Rates in WD 1145+017 and other Polluted White Dwarf Systems, MNRAS, arXiv
    Tom Kaye presentation at 2016 Society for Astronomical Science meeting: link   

Related Links  
    Mukremin Kilic's pro/am search of dusty WDs for dips:  https://www.nhn.ou.edu/%7Ekilic/Docs/dusty.html
    Some observing "good practices" for amateurs (book): Exoplanet Observing for Amateurs
    Hereford Arizona Observatory (HAO):  http://www.brucegary.net/HAO/
    Tutorial for faint object observing techniques using amateur hardware: http://brucegary.net/asteroids/  
    Master list of my web pages & Resume

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WebMaster:   Nothing on this web page is copyrighted. This site opened:  2018 November 29