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 2019.05.24 23 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  
  Collision model thoughts   
  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: 

The following sequence of phase-folded light curves can be used to study the recent evolution of all dip activity.






Noisy due to full moon











The following 3 waterfall plots show dip phase using an ephemeris for the A-fragments.








The following 3 waterfall plots show dip phase using an ephemeris for the D-fragments.







The next 3 lots show dust production "activity" level vs. date.







List of observing sessions   

2019.05.24 - BG16 
2019.05.21 - BG16  
2019.05.18 - BG16  
2019.05.12 - BG16  
2019.05.11 - BG16  
2019.05.08 - BG16  
2019.05.05 - BG16  
2019.05.04 - TK16  
2019.05.02 - BG16  
2019.04.28 - BG16  
2019.04.25 - BG16  
2019.04.24 - BG16 
2019.04.23 - BG16 
2019.04.21 - TK16
2019.04.21 - BG16
2019.04.13 - BG14  
2019.04.11 - BG14  
2019.04.09 - BG14 
2019.04.08 - BG14  
2019.04.03 - TK32 
2019.04.03 - TK16 
2019.04.03 - BG15  
2019.04.02 - TK16  
2019.03.29 - TK32 
2019.03.29 - TK16 
2019.03.29 - BG14 
2019.03.24 - BG14 
2019.03.23 - BG14
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  


2019.05.24 - BG16  







2019.05.21 - BG16  









2019.05.18 - BG16  

Nearby full moon increased noise level.









2019.05.12 - BG16  

Clouds before and after a short clearing provided ~ 1/2 orbit coverage. But it can be combined with data from the night before to provide ~ a full orbit of coverage.









2019.05.11 - BG16  

Clouds before and after a short clearing provided < 1 orbit coverage.



2019.05.08 - BG16  









2019.05.05 - BG16  





2019.05.04 - TK16  







2019.05.02 - BG16  









2019.04.28 - BG16     









2019.04.25 - BG16  









2019.04.24 - BG16 








Notice several events of cloud losses, as much as 1.5 mag's. 

2019.04.23 - BG16 

This is the second observation with my new telescope. It's short because I'm calibrating other properties of the hardware, but the data indicates that quality is improved over what my Meade 14" provided.





2019.04.21 - TK16 

Warm WX, and darks not at same temp as lights so cal did poor job.









2019.04.21 - BG16 

This is the first LC I made with a new telescope, an Astro-Tech 16" Ritchey-Chretien.








This is the first LC made with a new telescope, an Astro-Tech 16" Ritchey-Chretien. It was windy most of the night, so data quality suffered.

2019.04.13 - BG14  









2019.04.11 - BG14 









2019.04.09 - BG14  









2019.04.08 - BG14  









2019.04.03 - TK32 



2019.04.03 - TK16  











2019.04.03 - BG14  








Wind degraded several images. A few clouds were also present.

2019.04.02 - TK16 









2019.03.29 - TK32


9 % outliers removed.

 


This LC has 9 % outliers removed.







 


2019.03.29 - TK16 







2019.03.29 - BG14 







2019.03.24 - BG14









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.


Figure M03. Diagram, to scale, of the Kepler A, D and B orbits, looking "down" from a "pole", including the 2015/16 dips associated with the Kepler A period, located at random orbit asimuths but at their true orbit distances. The shape, labeled "Most common dip size," corresponds to a dip size that produces a dip depth of 30 % (which was comon for that season). Since particles ejected with velocity components for and aft are orbitally sheared to greater and smaller azimuth values they define an oval shape that would keep expanding if those particles didn't sublimate out of existence.   

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


Figure M04. Waterfall plot for the 2017/18 observing season, using the A ephemeris (as described in Rappaport, 2018).


Figure M05. Waterfall plot for the current observing season, using the A ephemeris (as described in Rappaport, 2018).


Figure M06. 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.

Collision Modeling

The paper by Su, Jackson & 15 others (download), presents a model for a young star's debris disk thermal emission variations that has possible use in explaining WD1145 transit fades. Although the paper's purpose is to account for IR thermal emission from the debris disk, the same model could be used to explain transit fadings of the star by such a disk if it was inclined edge-on.

The WD1145 discovery paper (Vanderburg et al, 2015) suggested that the transiting dust clouds are produced by the sublimation planetesimals (in the 5 Kepler orbits). Ever since this model was under consideration there has been no credible mechanism to account for the large ejection velocities of the particles in such clouds. Note that this model assumes quasi-continuous production of dust due to sublimation jets that eject overlying dust. Each dust particle would then have a ejection location that its new orbit would pass through. Particles ejected vertically would be in inclined orbits with maximum vertical extent determined by the ejection speed, and their orbital period would be unchanged. The particle would pass through the planetesimal's orbit plane, close to the planetesimal, twice per orbit. Particles ejected toward the WD, or away from it, would be in eccentric orbits confined to the planetesimal orbit plane, and their orbital period would be unchanged. The maximum radial extent of the motion pf these particles would also depend on the ejection velocity. Particles ejected in the forward and backward directions (i.e., along the planetesimal's orbit motion) would be in eccentric orbits with different periods; those ejected forward would have their periastron at the ejection location and those ejected backward would have their apoastron at the ejection site. Because these fore/aft ejections lead to different orbit periods these particles would undergo "orbit shear" (also referred to as "Keplerian shear"), and they would spread along the orbit in both directions. Since the other two ejection geometries are not associated with a change in orbit period those particles would remain within a volume, approximately spherical, until they interacted with something to change their orbits (such as radiation pressure, or collisions, or Poynting-Robertson drag).
 
So far there is nothing exotic about the above scenario; the big problem is that sublimation jets are thought to be incapable of ejection velocities needed to account for the observed dust cloud sizes. Dips are typically 4 minutes in duration, which corresponds to a size that is ~ 5 times the WD disk diameter. We've observed dip depths of > 60% on a few occasions. If the dust clouds are opaque (with abrupt edges) then we can consider them to have the shape of a band crossing the WD disk. If the obstructing dust cloud is a band that crossd disk center, then to produce a 60 % blockage the vertical width of the dust cloud would have to be 0.50 x WD diameter. This would require that some particles are in inclined orbits that extend to the + and - 0.50 WD radius locations. For particles to reach those heights above the planetesimal orbit plane they would have to be ejected with a speed of 1.5 km/s. So far no one has made a case for sublimation jets being able to achieve these speeds.

Collisions, on the other hand, can achieve speeds of these amounts easily [need a reference for this]. If a dust cloud was produced by a collision all dust particles (with the same period) would be in orbits that return them to the collision location every orbit! In addition, the same coming together occurs for the anti-collision location (we're assuming circular orbits). In other words, the dust cloud wouold expand and contract twice per orbit, but since the Earth's line-of-sight to the WD is for just one orbit location we will observe the dust cloud when it is at the same phase of its expansion/contraction cycle, and it will therefore produe the same dip depth. The foregoing neglects the orbit shear by particles ejected in the fore/aft directions, but let's worry about that later. Note that for the original mechanism producing the dust clouds, sublimation jets, the ejection locations for particles with the same period will be spread out uniformly around the planetesimal's orbit. The dust cloud can remain the same size throughout its orbit even though the particles are constantly moving throughout the cloud.
























Data Exchange Files   

    2015.11.21 to 2016.07.15  
    2016.10.25 to 2017.06.18  
    2017.11.10 to 2018.06.18 
    2018.11.09 to 2019.03.15  (request webmaster) 


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


    Xu, Siyi, Na'ama Hallokoun, Bruce Gary, Paul Dalba, John Debes and 14 others, 2019, "Shallow Ultraviolet Transits of WD 1145+017," arXiv 
    Gansicke, Boris + 26 others, 2019, "Evolved Planetary Systems around White Dwarfs," Astro 2020 Science White paper, arXiv
    Manser, Christopher + 31 others, 2019, "A Planetesimal Orbiting the Debris Disk around a White Dwarf Star," arXiv
    Veras, Dimitri + 8 others, 2019, "Orbital Relaxation and Excitation of Planets Tdally Interacting with White Dwarfs," arXiv  
    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