First observed with the Kepler mission, KIC 8462852 undergoes unexplained dimming events, "dips," on the timescale of days which were again observed from the ground from May to December 2017. Monitored with multi-band photometry by the Los Cumbres Observatory, all four dips of the "Elsie dip family" display clear wavelength dependence. We measure how the wavelength dependence changes over the whole dimming event, including the dimming between the dips and the brightening event (the `blip') which occurs after the dips. We find that a single wavelength dependence does not fit the entire light curve and the dimming occurring between the dips is non-gray and varies in time. Because of the non-gray dimming between the dips, we measure the wavelength dependence of the dips separately and without the extra depth from this dimming. Such measurements yield a different estimate of the wavelength dependence the wavelength dependence of the dips but remains consistent with the previous measurement except for Elsie (the first dip), which is surrounded by dimming with strong wavelength dependence. We find the range of the wavelength dependence variation of the entire 2017 light curve is consistent with optically-thin dust with an average radius of r<1μm and the dust causing just the dips being r<0.5μm. Since the dependence is time-dependent, the dust occulting the star must be heterogeneous in size, composition, or both and the distributions of these properties along the line of sight must change over time.
VVV-WIT-07: another Boyajian’s star or a Mamajek’s object?We report the discovery of VVV-WIT-07, an unique and intriguing variable source presenting a sequence of recurrent dips with a likely deep eclipse in July 2012. The object was found serendipitously in the near-IR data obtained by the VISTA Vari- ables in the V ́ıa La ́ctea (VVV) ESO Public Survey. Our analysis is based on VVV variability, multicolor, and proper motion (PM) data. Complementary data from the VVV eXtended survey (VVVX) as well as archive data and spectroscopic follow-up observations aided in the analysis and interpretation of VVV-WIT-07. A search for periodicity in the VVV Ks-band light curve of VVV-WIT-07 results in two tentative periods at P ∼ 322 days and P ∼ 170 days. Colors and PM are consistent either with a reddened MS star or a pre-MS star in the foreground disk. The near-IR spectra of VVV-WIT-07 appear featureless, having no prominent lines in emission or absorption. Features found in the light curve of VVV-WIT-07 are similar to those seen in J1407 (Mamajek’s object), a pre-MS K5 dwarf with a ring system eclipsing the star or, al- ternatively, to KIC 8462852 (Boyajian’s star), an F3 IV/V star showing irregular and aperiodic dips in its light curve. Alternative scenarios, none of which is fully consistent with the available data, are also briefly discussed, including a young stellar object, a T Tauri star surrounded by clumpy dust structure, a main sequence star eclipsed by a nearby extended object, a self-eclipsing R CrB variable star, and even a long-period, high-inclination X-ray binary.
We describe EPIC 205718330 and EPIC 235240266, two systems identified in the K2 data whose light curves contain episodic drops in brightness with shapes and durations similar to those of the young "dipper" stars, yet shallower by ~1-2 orders of magnitude. These "little dippers" have diverse profile shapes with durations of ~0.5-1.0 days and depths of ~0.1-1.0% in flux; however, unlike most of the young dipper stars, these do not exhibit any detectable infrared excess indicative of protoplanetary disks, and our ground-based follow-up spectra lack any signatures of youth while indicating these objects as kinematically old. After ruling out instrumental and/or data processing artifacts as sources of the dimming events, we investigate possible astrophysical mechanisms based on the light curve and stellar properties. We argue that the little dippers are consistent with transits of star-grazing exocomets, and speculate that they are signposts of massive non-transiting exoplanets driving the close-approach orbits.
In 2010, the Vista Variables in the Via Lactea (VVV) survey began its project of creating a three-dimensional map of variable stars in the vicinity of the Milky Way’s center. As part of the project, astronomer Roberto Saito of the Federal University of Santa Catarina scoured the telescope’s data for eruptive outbursts from the hundreds of millions of monitored stars. But the most notable thing he found was not an outburst at all—it was a star that grew mysteriously dim over several days in 2012. He and his colleagues reported their findings in a recently published paper in the Monthly Notices of the Royal Astronomical Society.Known as VVV-WIT-07, the star appears to be much older and redder than our sun, although the amount of interstellar dust between our solar system and the star’s home closer to the galactic center makes exact classification and distance measurements very difficult. What is certain is that in the summer of 2012, the object's brightness faded slightly for 11 days, then plummeted over the following 48 days, suggesting that something blocked more than three quarters of the star’s light streaming toward Earth. But what could that “something” be?
Boyajian's star is an apparently normal main sequence F-type star with a very unusual light curve. The dipping activity of the star, discovered during the Kepler mission, presents deep, asymmetric, and aperiodic events. Here we present high resolution spectroscopic follow-up during some dimming events recorded post-Kepler observations, from ground-based telescopes. We analise data from the HERMES, HARPS-N and FIES spectrographs to characterise the stellar atmosphere and to put some constraints on the hypotheses that have appeared in the literature concerning the occulting elements. The star's magnetism, if existing, is not extreme. The spots on the surface, if present, would occupy 0.02% of the area, at most. The chromosphere, irrespective of the epoch of observation, is hotter than the values expected from radiative equilibrium, meaning that the star has some degree of activity. We find no clear evidence of the interstellar medium nor exocoments being responsible for the dimmings of the light curve. However, we detect at 1-2 sigma level, a decrease of the radial velocity of the star during the first dip recorded after the Kepler observations. We claim the presence of an optically thick object with likely inclined and high impact parameter orbits that produces the observed Rossiter-McLaughlin effect.
If you remove the "?s=21" from the end of the url, it should work I think [ I'll then delete this comment :-) ]
Quote from: jebbo on 12/19/2018 07:08 amIf you remove the "?s=21" from the end of the url, it should work I think [ I'll then delete this comment :-) ]Thanks for that suggestion. I edited to effect that change and it appears to work. Leaving this post here to benefit others.
"We analyse 177 high-resolution spectra of Boyajian's Star in an effort to detect potential laser signals from extraterrestrial civilisations," the researchers wrote in their paper.Using data from the Lick Observatory's Automated Planet Finder telescope, the team looked for continuous laser light more powerful than 24 megawatts. That's the lower limit of power detectable by the telescope at 1,470 light-years away - the distance to KIC 8462852.
First identified more than a century ago, the star dips in brightness over days or weeks before recovering to its previous luminosity. At the same time, the star appears to be slowly losing its luster overall, leaving researchers scratching their heads.Now, astronomers at Columbia University believe they’ve developed an explanation for this oddity.In a new paper published in the Monthly Notices of the Royal Astronomical Society, astrophysicists Brian Metzger, Miguel Martinez and Nicholas Stone propose that the long-term dimming is the result of a disk of debris – torn from a melting exomoon – that is accumulating and orbiting the star, blocking its light as the material passes between the star and Earth.
One would think an actual extrasolar planet should have been discovered transiting the star considering the amount of observations that have been done if an exomoon is causing this.
Quote from: Orbiter on 09/16/2019 07:46 pmOne would think an actual extrasolar planet should have been discovered transiting the star considering the amount of observations that have been done if an exomoon is causing this.I believe that article mentions that the planet would have been ejected fri the system in the process of capturing the moon.