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The First Post-Kepler Brightness Dips of KIC 8462852
We present a photometric detection of the first brightness dips of the unique
variable star KIC 8462852 since the end of the Kepler space mission in 2013
May. Our regular photometric surveillance started in October 2015, and a
sequence of dipping began in 2017 May continuing on through the end of 2017,
when the star was no longer visible from Earth. We distinguish four main 1-2.5%
dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on
timescales from several days to weeks. Our main results so far are: (i) there
are no apparent changes of the stellar spectrum or polarization during the
dips; (ii) the multiband photometry of the dips shows differential reddening
favoring non-grey extinction. Therefore, our data are inconsistent with dip
models that invoke optically thick material, but rather they are in-line with
predictions for an occulter consisting primarily of ordinary dust, where much
of the material must be optically thin with a size scale <<1um, and may also be
consistent with models invoking variations intrinsic to the stellar
photosphere. Notably, our data do not place constraints on the color of the
longer-term "secular" dimming, which may be caused by independent processes, or
probe different regimes of a single process
Special cases : moons, rings, comets, trojans
Non-planetary bodies provide valuable insight into our current under-
standing of planetary formation and evolution. Although these objects are
challeng- ing to detect and characterize, the potential information to be drawn
from them has motivated various searches through a number of techniques. Here,
we briefly review the current status in the search of moons, rings, comets, and
trojans in exoplanet systems and suggest what future discoveries may occur in
the near future.Comment: Invited review (status August 2017
Extrasolar enigmas: from disintegrating exoplanets to exoasteroids
Thousands of transiting exoplanets have been discovered to date, thanks in
great part to the {\em Kepler} space mission. As in all populations, and
certainly in the case of exoplanets, one finds unique objects with distinct
characteristics. Here we will describe the properties and behaviour of a small
group of `disintegrating' exoplanets discovered over the last few years (KIC
12557548b, K2-22b, and others). They evaporate, lose mass unraveling their
naked cores, produce spectacular dusty comet-like tails, and feature highly
variable asymmetric transits. Apart from these exoplanets, there is
observational evidence for even smaller `exo-'objects orbiting other stars:
exoasteroids and exocomets. Most probably, such objects are also behind the
mystery of Boyajian's star. Ongoing and upcoming space missions such as {\em
TESS} and PLATO will hopefully discover more objects of this kind, and a new
era of the exploration of small extrasolar systems bodies will be upon us.Comment: Accepted for publication in the book "Reviews in Frontiers of Modern
Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka;
publisher Springer Nature) funded by the European Union Erasmus+ Strategic
Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556
BINARY CENTRAL STARS OF PLANETARY NEBULAE DISCOVERED THROUGH PHOTOMETRIC VARIABILITY. IV. THE CENTRAL STARS OF HaTr 4 AND Hf 2-2
We explore the photometrically variable central stars of the planetary nebulae HaTr 4 and Hf 2-2. Both have been classified as close binary star systems previously based on their light curves alone. Here, we present additional arguments and data confirming the identification of both as close binaries with an irradiated cool companion to the hot central star. We include updated light curves, orbital periods, and preliminary binary modeling for both systems. We also identify for the first time the central star of HaTr 4 as an eclipsing binary. Neither system has been well studied in the past, but we utilize the small amount of existing data to limit possible binary parameters, including system inclination. These parameters are then compared to nebular parameters to further our knowledge of the relationship between binary central stars of planetary nebulae and nebular shaping and ejection
The first post-Kepler brightness dips of KIC 8462852
We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in 2015 October, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1%–2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor," which persist on timescales from several days to weeks. Our main results so far are as follows: (i) there are no apparent changes of the stellar spectrum or polarization during the dips and (ii) the multiband photometry of the dips shows differential reddening favoring non-gray extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale Lt1 μm, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process