WD1145 HAO

2 of 10 - 2016.01.17 to 2016.07.13: LC Observations - 2nd set of LCs, for 2015/16 observing season
3 of 10 - 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 10 - 2016.10.25 to 2017.06.18: LC Observations - 4th set of LCs, for 2016/17 observing season
5 of 10 - 2017.10.23 to 2018.06.19: LC Observations - 5th set of LCs, for 2017/18 observing season
6 of 10 - 2018.11.06 to 2019.07.09 LC Observations - 6th set of LCs, for 2018/19 observing season
Previous observing seasons summary of results:    Observational findings that need to be explained by models
7 of 10 - 2019.12.02 to 2020.07.09   LC Observations -   7th set of LCs, for 2019/20 observng season
8 of 10 - 2020.11.19 to 2021.06.07 LC Observations - 8th set of LCs, for 2020/21 observing season
9 of 10 - 2021.12.12 to 2022.07.16 LC Observations -   9th set of LCs, for 2021/22 observing season
10 of 11 - 2022.11.21 to 2023.06.12 LC Observations - 10th set of LCs, for 2022/23 observing season
11 of 11 - 2023.12.25 to present     LC Observations - 11th set of LCs, for 2023/24 observing season (YOU ARE HERE)

Links on this web page:
Status & summary of results for recent observations
Activity Plots
Kepler K2 observations analysis   (external web page)
Waterfall plots for date groups   (external web page)
List of observing session dates
Observing session LCs
Finder image & basic info
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 level of dip activity during this observing season is the lowest for all ground-based observations during the past 10 years, and similar to what was observed by Kepler in 2014.

Waterfall Plot

The graphs below are waterfall plots.

Figure 1. This waterfall plot is for March, and it shows the appearance of a dip on Mar 2 or 3 that has a period of 4.500 hours, which is the same as measured using Kepler data 10 years ago.
The Mar 11 LC had missing data exactly when the dip was expected.

Activity Plots

The next 3 graphs show the level of "dust production dip activity" vs. date:

Figure 2. Dip activity for this season, and last year's.

Figure 3. Dip activity for the first 4 season's of ground-based measurements. The sinusoidal trace (tan, at bottom) has a period of 0.34 yeaar, 124 days), and it is correlated with activity measurements. The black trace that fits data was produced by a repeating pattern of Gaussian shapes with height and widths adjustments . Small date shifts were applied to improve fitting.

Figure 4. Same as above, but covering all 10 years of ground-based measurements. The repeating Gaussian model was discontinued after the 2021 season due to an activity level that was insufficient for fitting.

Figure 5. Activity for the last 11 years, using a log scale for activity. The thick green trace is a Poisson function (lamda = 2) with an ever-present 0.25 % activity level added.

Here's an orbit model that can produce a 124-day periodicity:

Figure 6. A planet in a highly elliptical orbit (e = 0.975) with a 124-day period would have a periastron that is just inside the A- through F-systems of fragments and associated dust clouds.

If a planet exists in the above orbit it could perturb the orbits of one or more fragments during each periastron passage. This might initiate a cascade of collisions that produce dust clouds. If the probability for collision abruptly rises and slowly falls according to a Poisson distribution, the shape of activity versus date could appear Gaussian with a full-width-at-half-maximum close to the observed value of ~ 60 days. The date of each cascade initiation can be slightly different each periastron passage, and this will cause the 124-day spacing of activity humps to differ somewhat from 124 days (which we observe). (Incidentally, the same could apply to J0139+5245, which has activity peaks spaced ~ 107 days apart, with a spacing variation that ranges from about 104 to 115 days. In fact, J0139 and WD1145 could both have an interloper in a large and highly eccentric orbit that perturbs a system of fragments shed by asteroids in a set of small and circular orbits.)

As the interloper's orbit slowly shrinks (to eventually become circular) it will have close encounters with fragments in the A-F systems. Imagine that after each interloper's periastron passage a few fragments undergo orbit changes. Some of them will collide with other fragments, and this will initiate a cascade of collisions, each producing a dust cloud, and after many orbits all inevitable collisions will slowly subside to none (appearing as an activity hump with FWHM ~ 60 days). For example, if there are 1000 fragments in the A-system, and 10 of them undergo orbit changes that lead to collisions after the interloper's periastron passage, 990 of them weren't at risk of collisions during the cascade. During the next 124 days the A-system planetesimal (asteroid?) sheds ~ 10 fragments due to tidal disruption (due to its slow orbit shrinkage). At the time of the next interloper periastron passage there will be 1000 fragments in the A-system, and almost all of them will be in orbits that don't intersect (except at a 0.25 % flux loss per orbit activity level). During a hypothetical 2nd periastron passage the interloper will pass close to fewer fragments than during the previous passage (because the 990 fragments are the ones less likely to have been passed close to by the interloper's first passage). Some of the 990 fragments will be in different parts of their orbit during the 2nd passage, so some of them will be perturbed into orbits that collide with other fragments (producing another 60-day hump in dip activity). Actually, there could be more orbit perturbations during a 2nd passage than the first, so a peak of activity might require 2 or 3 periastron passages of the interloper to achieve the most activity (c.f., Fig. 5). However, each subsequent periastron passage will be accompanied by an exhausting probability for the interloper to perturb an A-system fragment. This scenario can probably be described by a Poisson distribution, as shown in Figure 5.

According to Figure 5 we are now in a stable orbit configuration: the interloper isn't perturbing A-system fragments, and the 1000 A-system fragments aren't colliding with each other. But the interloper orbit is shrinking, and it's changing periastron path (and timing) will be able to interact differently with A-system fragments. New A fragment perturbations will be possible, and a new cycle of "activity rise and fall" will be possible. How long are the intervals between Figure 5 Poisson patterns? I don't know! Hopefully, this can be answered using celestial mechanic models.The first step is to refine such models using the activity behaviors already determined from measurements.

List of observing sessions