Extinction and the Dimming of KIC 8462852

Extinction and the Dimming of KIC 8462852

Authors:

Meng et al

Abstract:

To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star over a wide wavelength range from the UV to the mid-infrared from 2015 October through 2016 December, using Swift, Spitzer and AstroLAB IRIS. The star faded in a manner similar to the long-term fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period reported is 22.1 ± 9.7 mmag yr−1 in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in the ground-based B measurements, 14.0 ± 4.5 mmag in V, and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2 mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at gsim3σ by three different observatories operating from the UV to the IR. The presence of long-term secular dimming means that previous spectral energy distribution models of the star based on photometric measurements taken years apart may not be accurate. We find that stellar models with ${T}_{\mathrm{eff}}=7000\mbox{--}7100$ K and ${A}_{V}\sim 0.73$ best fit the Swift data from UV to optical. These models also show no excess in the near-simultaneous Spitzer photometry at 3.6 and 4.5 μm, although a longer wavelength excess from a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of the fading favors a relatively neutral color (i.e., ${R}_{V}\gtrsim 5$, but not flat across all the bands) compared with the extinction law for the general interstellar medium (${R}_{V}=3.1$), suggesting that the dimming arises from circumstellar material.

A 1574-day periodicity of transits orbiting KIC 8462852

A 1574-day periodicity of transits orbiting KIC 8462852

Authors:

Sacco et al

Abstract:
Observations of the main sequence F3 V star KIC 8462852 (also known as Boyajian's star) revealed extreme aperiodic dips in flux up to 20% during the four years of the Kepler mission. Smaller dips (< 2%) were also observed with ground-based telescopes between May and September 2017. We investigated possible correlation between recent dips and the major dips in the last 100 days of the Kepler mission. We compared Kepler light curve data, 2017 data from two observatories (TFN, OGG) which are part of the Las Cumbres Observatory (LCO) network and Sternberg observatory archival data, and determined that observations are consistent with a 1,574-day (4.31 year) periodicity of a transit (or group of transits) orbiting Boyajian's star within the habitable zone. It is unknown if transits that have produced other major dips as observed during the Kepler mission (e.g. D792) share the same orbital period. Nevertheless, the proposed periodicity is a step forward in guiding future observation efforts.

Optical Polarimetry of KIC 8462852 in May-August 2017

Optical Polarimetry of KIC 8462852 in May-August 2017 

Authors:

Steele et al

Abstract: 

We present optical polarimetry in the period May-August 2017 of the enigmatic "dipping" star KIC 8462852. During that period three ~1% photometric dips were reported by other observers. We measured the average absolute polarization of the source, and find no excess or unusual polarization compared to a nearby comparison star. We place tight upper limits on any change in the degree of polarization of the source between epochs in- and out-of-dip of less than 0.1% (8500-Ang.) and less than 0.2% (7050-Ang. and 5300-Ang.). How our limits are interpreted depends on the specific model being considered. If the whole stellar disk were covered by material with an optical depth of ~0.01 then the fractional polarisation introduced by this material must be less than 10-20%. While our non-detection does not constrain the comet scenario, it predicts that even modest amounts of dust that have properties similar to Solar System comets may be detectable. We note that the sensitivity of our method scales with the depth of the dip. Should a future ~20% photometric dip be observed (as was previously detected by Kepler) our method would constrain any induced polarization associated with any occulting material to 0.5-1.0%.

Detection of a repeated transit signature in the light curve of the enigma star KIC 8462852: a 928-day period?

Detection of a repeated transit signature in the light curve of the enigma star KIC 8462852: a 928-day period?

Authors:

Kiefer et al

Abstract:
As revealed by its peculiar Kepler light curve, the enigmatic star KIC 8462852 undergoes short and deep flux dimmings at a priori unrelated epochs. It presents nonetheless all other characteristics of a quiet 1 Gyr old F3V star. These dimmings resemble the absorption features expected for the transit of dust cometary tails. The exocomet scenario is therefore most commonly advocated. We reanalyzed the Kepler data and extracted a new high-quality light curve to allow for the search of shallow signature of single or a few exocomets. We discovered that among the 22 flux dimming events that we identified, two events present a striking similarity. These events occurred 928.25 days apart, lasted for 4.4 days with a drop of the star brightness by 1000 ppm. We show that the light curve of these events is well explained by the occultation of the star by a giant ring system, or the transit of a string of half a dozen of exocomets with a typical dust production rate of 105-106 kg/s. Assuming that these two similar events are related to the transit of the same object, we derive a period of 928.25 days. The following transit was expected in March 2017 but bad weather prohibited us to detect it from ground-based spectroscopy. We predict that the next event will occur from the 3rd to the 8th of October 2019.

Where's the Flux? The Official Page of the Investigations into Tabby's

There is an official Website for the investigations into Tabby's Star, the mysteriously fading star.

Could Tabby's Star's Dimming be due to a Ring of Debris in OUR Solar System?

Tabetha's Rings

Author:

Katz

Abstract:
Could the dips of "Tabetha's Star" (KIC 8462852) have been caused by matter in our Solar System? The interval between periods of deep dips is nearly twice the orbital period of the Kepler satellite. I consider a clumpy particulate ring in the outer Solar System that grazes the line of sight to the star once per orbit of Kepler. The hypothesis predicts that future dips may be observed from Earth during windows separated by a year, although their detailed structure depends on the distribution of particles along the ring. Dips observed at separated sites will be decorrelated, with correlation lengths ≲1012 cm, and possibly as short as ∼600 m.

Did a Large Ringed Exoplanet With Trojans dim Tabby's Star?

KIC 8462852: Will the Trojans return in 2021?

Authors:

Ballesteros et al

Abstract:
KIC 8462852 stood out among more than 100,000 stars in the Kepler catalogue because of the strange features of its light curve: a wide and asymmetric dimming taking up to 15 per cent of the total light, together with a period of multiple, narrow dimmings happening approximately 700 days later. Several models have been proposed to account for this abnormal behaviour, most of which require either unlikely causes or a finely-tuned timing. We aim at offering a relatively natural solution, invoking only phenomena that have been previously observed, although perhaps in larger or more massive versions. We model the system using a large, ringed body whose transit produces the first dimming and a swarm of Trojan objects sharing its orbit that causes the second period of multiple dimmings. The resulting orbital period is T≈12 years, with a semi-major axis a≈6 au. Our model allows us to make two straightforward predictions: we expect the passage of a new swarm of Trojans in front of the star starting during the early months of 2021, and a new transit of the main object during the first half of 2023.

Did Tabby's Star Ingest an Exoplanet?

Secular dimming of KIC 8462852 following its consumption of a planet

Authors:

Metzger et al

Abstract:
The Kepler-field star KIC 8462852, an otherwise apparently ordinary F3 main-sequence star, showed several highly unusual dimming events of variable depth and duration. Adding to the mystery was the discovery that KIC 8462852 faded by 14 per cent from 1890 to 1989, as well as by another 3 per cent over the 4 yr Kepler mission. Following an initial suggestion by Wright & Sigurdsson, we propose that the secular dimming behaviour is the result of the inspiral of a planetary body or bodies into KIC 8462852, which took place ∼10–104 yr ago (depending on the planet mass). Gravitational energy released as the body inspirals into the outer layers of the star caused a temporary and unobserved brightening, from which the stellar flux is now returning to the quiescent state. The transient dimming events could then be due to obscuration by planetary debris from an earlier partial disruption of the same inspiralling bodies, or due to evaporation and outgassing from a tidally detached moon system. Alternatively, the dimming events could arise from a large number of comet- or planetesimal-mass bodies placed on to high-eccentricity orbits by the same mechanism (e.g. Lidov–Kozai oscillations due to the outer M-dwarf companion) responsible for driving the more massive planets into KIC 8462852. The required high occurrence rate of KIC 8462852-like systems that have undergone recent major planet inspiral event(s) is the greatest challenge to the model, placing large lower limits on the mass of planetary systems surrounding F stars and/or requiring an unlikely probability to catch KIC 8462852 in its current state.

Sonneberg Plate Photometry for Boyajian's Star in Two Passbands

Sonneberg Plate Photometry for Boyajian's Star in Two Passbands

Authors:

Hippke et al

Abstract:
The F3 main-sequence star KIC 8462852 (Boyajian's Star) showed deep (up to 20%) day-long brightness dips of unknown cause during the four years of the Kepler mission. A 0.164 mag (16%) dimming between 1890 and 1990 was claimed, based on the analysis of photographic plates from the Harvard Observatory. We have gathered an independent set of historic plates from Sonneberg Observatory, Germany, covering the years of 1934–1995. With 861 mag in B, and 397 mag in V, we find the star to be of constant brightness within 0.03 mag per century (3%). Consistent outcomes are found using by-eye estimates of the best 119 plates. Results are supported by data from Sternberg Observatory, Moscow, which show the star as constant between 1895 and 1995. The previously claimed century-long dimming is inconsistent with our results at the $5\sigma $-level, however, the recently reported modest dimming of 3% in the Kepler data is not inconsistent with our data. We find no periodicities or shorter trends within our limits of 5% per five year bin, but note a possible dimming event on 1978 October 24.

Is KIC 8462852 (Tabby's Star) Being Eclipsed by Four Dusty Exoplanets

Mysterious eclipses in the light-curve of KIC8462852: a possible explanation

Authors:

Neslusan et al

Abstract:

Apart from thousands of `regular' exoplanet candidates, Kepler satellite has discovered a few stars exhibiting peculiar eclipse-like events. They are most probably caused by disintegrating bodies transiting in front of the star. However, the nature of the bodies and obscuration events, such as those observed in KIC8462852, remain mysterious. A swarm of comets or artificial alien mega-structures have been proposed as an explanation for the latter object.

We explore the possibility that such eclipses are caused by the dust clouds associated with massive parent bodies orbiting the host star.

We assumed a massive object and a simple model of the dust cloud surrounding the object. Then, we used the numerical integration to simulate the evolution of the cloud, its parent body, and resulting light-curves as they orbit and transit the star.

We found that it is possible to reproduce the basic features in the light-curve of KIC8462852 with only four objects enshrouded in dust clouds. The fact that they are all on similar orbits and that such models require only a handful of free parameters provides additional support for this hypothesis.

This model provides an alternative to the comet scenario. With such physical models at hand, at present, there is no need to invoke alien mega-structures for an explanation of these light-curves.

Did KIC 8462852 (Tabby's Star) Dim Because it Consumed an Exoplanet?

Secular Dimming of KIC 8462852 Following its Consumption of a Planet

Authors:

Metzger et al

Abstract:

The Kepler-field star KIC 8462852, an otherwise apparently ordinary F3 main-sequence star, showed several highly unusual dimming events of variable depth and duration. Adding to the mystery was the discovery that KIC 8462852 faded by 14% from 1890 to 1989, as well as by another 3% over the 4 year Kepler mission. Following an initial suggestion by Wright & Sigurdsson, we propose that the secular dimming behavior is the result of the inspiral of a planetary body or bodies into KIC 8462852, which took place ~10 to 1e4 years ago (depending on the planet mass). Gravitational energy released as the body inspirals into the outer layers of the star caused a temporary and unobserved brightening, from which the stellar flux is now returning to the quiescent state. The transient dimming events could then be due to obscuration by planetary debris from an earlier partial disruption of the same inspiraling bodies, or due to evaporation and out-gassing from a tidally detached moon system. Alternatively, the dimming events could arise from a large number of bodies comet- or planetesimal-mass bodies placed onto high eccentricity orbits by the same mechanism (e.g. Lidov-Kozai oscillations due to the outer M-dwarf companion) responsible for driving the more massive planets into KIC 8462852. The required high occurrence rate of KIC 8462852-like systems which have undergone recent major planet inspiral event(s) is the greatest challenge to the model, placing large lower limits on the mass of planetary systems surrounding F stars and/or requiring an unlikely probability to catch KIC 8462852 in its current state.

The Weirdness of Enigma Star KIC 8462852 (Tabby's Star)

Photometric and astrometric vagaries of the enigma star KIC 8462852

Authors:

Makarov et al

Abstract:

We apply a PCA-based pre-whitening method to the entire collection of main Kepler mission long-cadence data for KIC 8462852 spanning four years. This technique removes the correlated variations of instrumental origin in both the detected light curves and astrometry, resolving intrinsic changes in flux and image position of less than 100 ppm and 1 mas, respectively. Beside the major dips in the light curve during mission quarters 8 and 16, when the flux dropped by up to 20%, we confirm multiple smaller dips across the time span of observation with amplitudes ranging from 0.1% to 7%. A variation of flux with a period of 0.88 d and a half-amplitude of approximately 90 ppm is confirmed in the PCA-cleaned data. We find that the phase of the wave is steady over the entire 15-month interval. We confidently detect a weak variability-induced motion (VIM) effect in the cleaned astrometric trajectories, when the moment-based centroids shift synchronously with the flux dips by up to 0.0008 pixels on the detector. The inconsistent magnitude and direction of VIM effects within the same quarter point at more than one source of photometric variability in the blended image. The 0.88 d periodicity comes from a different source, not from the target star KIC 8462852. We discuss a possible interpretation of the bizarre properties of the source as a swarm of interstellar junk (comets and planetoids) crossing the line of sight to the star and its optical companions at approximately 7 mas per year.

Beyond Extraordinary Claim: Tabby's Star is Being "Star Lifted" (aka Mined)

A physically inspired model of Dip d792 and d1519 of the Kepler light curve seen at KIC8462852

Authors:

Heindl et al

Abstract:

The star KIC 8462852 shows a very unusual and hard to comprehend light curve. The dip d7922 absorbs 16% of the starlight. The light curve is unusually smooth but the very steep edges make it hard to find a simple natural explanation by covering due to comets or other well-known planetary objects. We describe a mathematical approximation to the light curve, which is motivated by a physically meaningful event of a large stellar beam which generates an orbiting cloud. The data might fit to the science fiction idea of star lifting, a mining technology that could extract star matter. We extend the model to d1519 and d1568 using multiple beams and get an encouraging result that fits essential parts of the dips but misses other parts of the measured flux. We recommend further exploration of this concept with refined models.

KIC 8462852 (tabby's Star) Did not Dim Between 1934 and 1995

Sonneberg plate photometry in two colors for KIC 8462852: No dimming between 1934 and 1995

Authors:

Hippke et al

Abstract:

The F3 main sequence star KIC 8462852 has raised interest because of its mysterious day-long brightness dips, and an unusual ~3% brightness decrease during the 4 years of the Kepler mission. Recently, a 0.164mag (~14%) dimming between 1890 and 1990 was claimed, based on the analysis of photographic plates, although this has been refuted. To resolve this controversy, we have gathered an independent set of historic data from Sonneberg Observatory, Germany. From these historic plates, we could extract 862 magnitudes in blue light, and 401 magnitudes in red light. The data cover the years 1934 to 1995 and are very evenly sampled between 1956 and 1995. In both colors, we find the star to be of constant brightness within 0.033mag/century (~3%). The previously claimed dimming is inconsistent with these data at the ∼5σ-level, however the recently reported modest dimming of ~3% in the Kepler data is not inconsistent with these data. We have also searched for periodicities and yearly trends in the data and find none within our limits of ~10% per year.