# Thread: Up to 22% Dips Detected in Starlight 1,500 LY Away

1. Good points, but I am content with the way it was put.

2. Without dragging this thread too far off course...
<derail>
Discovering a Dyson Sphere 1500ly away would be very bad IMO.

Not from them, but from ourselves.

It would be seen as a threat to humans of cosmic proportions. Whole factions would go into Doomsday Prepper mode - with a shift in economy large enough to change the face of civilization.

(Of course, it might also spark a new age of cooperation and technological discovery - whether for space travel, or home defense, I'm not sure.)

</derail>

3. Originally Posted by Roger E. Moore
Good points, but I am content with the way it was put.
I'm just a little bit curious, because DaveC426913 wrote:

It would be seen as a threat to humans of cosmic proportions. Whole factions would go into Doomsday Prepper mode - with a shift in economy large enough to change the face of civilization.
For me it wouldn't be a big deal, but you mentioned something pretty close to what was stated there. Do you think that you would go into Doomsday Prepper mode if we did find that there was a Dyson Sphere around the star. For me it would be more like, "cool!"

4. Maybe it's more telling of the human(s) making the doomsday statements than of any purported aliens. Why is the assumption they'd be anything like us, in the conquest regard? I agree with Jens... COULD rather than WOULD. Might that "could" drive so many of us into panic to collapse the current world order? I doubt it. It'd be a watershed time for humanity, sure, but I don't think it would automatically be that terrible. But, as with all speculation, "YMMV".

CJSF

5. Data time. 2018 was a good year for this star, and more news is sure to come (several posts to follow).

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Sandford, Emily; Kipping, D.
07/2018

The light curves of transiting exoplanets are rich in information. If we assume a physical model for an exoplanet--usually, a spherical body in a Keplerian orbit about a host star--we may then infer the parameters of this model, including physical properties of the planet, its orbit, and the host star, directly from the light curve. However, anomalous transit-like events, such as those observed in star KIC 8462852 (Boyajian et al. 2016), resist this type of analysis, because their physical cause, and consequently the appropriate model, is not apparent. Here, we present a novel approach to modeling the shape of a transiting object from its light curve alone, in which we assume no physical model for the object. We instead model the object as a grid of pixels which transits the star; each pixel has an opacity, ranging from transparent to opaque. We infer these opacities directly from the light curve using the Simultaneous Algebraic Reconstruction Technique (Andersen & Kak 1984), an algorithm developed for medical tomographic imaging, and thus generate an image of the transiting object.

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[Added in case anyone can access the data and study it.]

VizieR Online Data Catalog: KIC 8462852 one-yr obs. from UV to MIR (Meng+, 2017)

Meng, H. Y. A.; Rieke, G.; Dubois, F.; Kennedy, G.; Marengo, M.; Siegel, M.; Su, K.; Trueba, N.; Wyatt, M.; Boyajian, T.; Lisse, C. M.; Logie, L.; Rau, S.; Vanaverbeke, S.
06/2018

KIC 8462852 was first observed by Swift/UVOT on 2015 October 22 and then approximately every three days from 2015 December 4 to 2016 March 27. X-ray data were obtained simultaneously with the Swift/XRT. Optical observations in B, V, and R bands were taken with the 684mm aperture Keller F4.1 Newtonian New Multi-Purpose Telescope (NMPT) of the public observatory AstroLAB IRIS, Zillebeke, Belgium. The B, V, and R filters are from Astrodon Photometrics, and have been shown to reproduce the Johnson/Cousins system closely. The earliest observation was made on 2015 September 29. There is a gap in time coverage from 2016 January 8 to June 8. We report the observations through 2016 December. Our first Spitzer/IRAC observation was executed on 2016 January 16. There is a gap in the time baseline of the monitoring in the period from 2016 April to July (from MJD 57475 to 57605) when KIC 8462852 was out of the visibility window of Spitzer. (3 data files).

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The KIC 8462852 Light Curve From 2015.75 to 2018.18 Shows a Variable Secular Decline

Schaefer, Bradley E.; Bentley, Rory O.; Boyajian, Tabetha S.; Coker, Phillip H.; Dvorak, Shawn; Dubois, Franky; Erdelyi, Emery; Ellis, Tyler; Graham, Keith; Harris, Barbara G.; Hall, John E.; James, Robert; Johnston, Steve J.; Kennedy, Grant; Logie, Ludwig; Nugent, Katherine M.; Oksanen, Arto; Ott, John J.; Rau, Steve; Vanaverbeke, Siegfried; van Lieshout, Rik; Wyatt, Mark
06/2018

The star KIC 8462852 (Boyajian's Star) displays both fast dips of up to 20% on time scales of days, plus long-term secular fading by up to 19% on time scales from a year to a century. We report on CCD photometry of KIC 8462852 from 2015.75 to 2018.18, with 19,176 images making for 1,866 nightly magnitudes in BVRI. Our light curves show a continuing secular decline (by 0.023±0.003 mags in the B-band) with three superposed dips with duration 120-180 days. This demonstrates that there is a continuum of dip durations from a day to a century, so that the secular fading is seen to be by the same physical mechanism as the short-duration Kepler dips. The BVRI light curves all have the same shape, with the slopes and amplitudes for VRI being systematically smaller than in the B-band by factors of 0.77±0.05, 0.50±0.05, and 0.31±0.05. We rule out any hypothesis involving occultation of the primary star by any star, planet, solid body, or optically thick cloud. But these ratios are the same as that expected for ordinary extinction by dust clouds. This chromatic extinction implies dust particle sizes going down to ˜0.1 micron, suggesting that this dust will be rapidly blown away by stellar radiation pressure, so the dust clouds must have formed within months. The modern infrared observations were taken at a time when there was at least 12.4%±1.3% dust coverage (as part of the secular dimming), and this is consistent with dimming originating in circumstellar dust.

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KIC 8462852: Maria Mitchell Observatory Photographic Photometry 1922 to 1991

Castelaz, M.; Barker, T.
06/2018

A new study of the long-term photometric behavior of the unusual star KIC 8462852 (Boyajian's Star) has been carried out using archival photographic plates from 1922Ã±1991 taken at the Maria Mitchell Observatory (MMO). We find five episodes of sudden, several day, decreases in magnitude occurring in 1935, 1966, 1978, and two in 1980. Episodes of sudden increase in magnitude appear to occur in 1967 and 1977. Inspection of archival light curves of KIC 8462852 from two previous studies based on the Harvard and the Sonneberg plate collections finds apparent corresponding events to these observed episodes in the MMO light curve. Also, a general trend of 0.12 ± 0.02 magnitude per century decrease is observed in the MMO light curve, significant, but less than the trend of 0.164 ± 0.013 observed in the Harvard light curve.

A 1,574-Day Periodicity of Transits Orbiting KIC 8462852

Sacco, G.; Ngo, L. D.; Modolo, J.
06/2018

Observations of the main sequence F3V 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 (< 3%) were also observed with ground-based telescopes between May 2017 and May 2018. 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, as well as archival data from the Harvard College Observatory (HCO), Sonneberg Observatory, and Sternberg Observatory, and determined that observations appear consistent with a 1,574-day (4.31-year) periodicity of a transit (or group of transits) orbiting BoyajianÃ*s star within the habitable zone. Comparison with future observations is required to validate this hypothesis. Furthermore, 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.

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The Variable Wavelength Dependence of the Dipping event of KIC 8462852

Bodman, Eva; Wright, Jason; Boyajian, Tabetha; Ellis, Tyler
06/2018

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 $r<1\,\mu$m and the dust causing just the dips being $r<0.5\,\mu$m. 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.

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Multiband Lightcurve of Tabby's Star: Observations and Modeling

Yin, Yao; Wilcox, Alejandro; Boyajian, Tabetha S.
06/2018

Since March 2017, The Thacher Observatory in California has been monitoring changes in brightness of KIC 8462852 (Tabby's Star), an F-type main sequence star whose irregular dimming behavior was first discovered by Tabetha Boyajian by examining Kepler data. We obtained over 20k observations over 135 nights in 2017 in 4 photometric bands, and detected 4 dip events greater than 1%. The relative magnitude of each dip compared across our 4 different photometric bands provides critical information regarding the nature of the obscuring material, and we present a preliminary analysis of these events. The Thacher Observatory is continuing its monitoring of Tabby's Star in 2018.

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'Where's the flux' star: Where's the excess?

Meng, Huan; Boyajian, Tabetha; Kennedy, Grant; Lisse, Carey; Marengo, Massimo; Wright, Jason; Wyatt, Mark
05/2018

KIC 8462852 provides, in real time, the rare chance to observe cataclysmic events happening in a mature extrasolar planetary system. The Kepler light curve of the star sees two major dips 750 days apart with depths of 20%, as well as a number of smaller dips ( 1%) at apparently random time. A series of new, shallow (2-4% in flux) dips has been observed since May 2017 and as late as March 2018. In addition to the days-long dips, the star has also been found to have long-term variations over years, and possibly centuries. Conclusions from existing observations suggest that the dips and long-term variations are likely caused by transits of dust clumps in front of the star. We have observed KIC 8462852 with Spitzer/IRAC since cycle 12. We propose to continue the monitoring in cycle 14 to track the long-term variations of the stellar flux, measure the optical properties of the transit dust, and look for possible transient excess if new dips happen close in time to our observations.
Last edited by Roger E. Moore; 2018-Aug-02 at 12:11 PM.

Recent photometric monitoring of KIC 8462852, the detection of a potential repeat of the Kepler day 1540 dip and a plausible model

Bourne, R.; Gary, B. L.; Plakhov, A.
04/2018

This paper presents V- and g΄-band observations of the F2V star KIC 8462852, which exhibited enigmatic fade patterns in Kepler mission data. We introduce a transit simulation model for interpretation of these fades, and use it to interpret a 2017 August dip as a repeat of the Kepler day 1540 dip (D1540). We suggest the 2017 August and D1540 dips may be caused by a brown dwarf and an associated ring system in a 1601-d elliptical orbit. Transiting icy moons of the proposed brown dwarf, sublimating near periapsis like comets, could provide an explanation for the significant dips observed by Kepler, as well as the recent 2017 May to October dips and the long-term variation in flux detected by Simon et al. Whereas the presence of such a ring structure is attractive for its ability to explain short-term fade events, we do not address how such a ring system can be created and maintained. This speculation predicted a brightening of ˜1 per cent that occurred during October 2017. In addition, this scenario predicts that a set of dimming events, similar to those in 2013 (Kepler) and in 2017 (reported here), can be expected to repeat during 2021 October to 2022 January and a repeat of D1540 should occur on 2021 December 27.

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Proper Motion of the Faint Star near KIC 8462852 (Boyajian's Star)---Not a Binary System

Clemens, Dan P.; Maheshwari, Kush; Jagani, Roshan; Montgomery, J.; El Batal, A. M.; Ellis, T. G.; Wright, J. T.
03/2018

A faint star located 2 arcsec from KIC 8462852 was discovered in Keck 10 m adaptive optics imaging in the JHK near-infrared (NIR) in 2014 by Boyajian et al. (2016). The closeness of the star to KIC 8462852 suggested that the two could constitute a binary, which might have implications for the cause of the brightness dips seen by Kepler and in ground-based optical studies. Here, NIR imaging in 2017 using the Mimir instrument resolved the pair and enabled measuring their separation. The faint star had moved 67 ± 7 milliarcsec (mas) relative to KIC 8462852 since 2014. The relative proper motion of the faint star is 23.9 ± 2.6 mas yr-1, for a tangential velocity of 45 ± 5 km s-1 if it is at the same 390 pc distance as KIC 8462852. Circular velocity at the 750 au current projected separation is 1.5 km s-1, hence the star pair cannot be bound.

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The GALEX View of Boyajian's Star'' (KIC 8462852)

Davenport, James. R. A.; Covey, Kevin R.; Clarke, Riley W.; Laycock, Zachery; Fleming, Scott W.; Boyajian, Tabetha S.; Montet, Benjamin T.; Shiao, Bernie; Million, Chase C.; Wilson, David J.; Olmedo, Manuel; Mamajek, Eric E.; Olmedo, Daniel; Chávez, Miguel; Bertone, Emanuele
02/2018

The enigmatic star KIC 8462852, informally known as `Boyajian's Star,'' has exhibited unexplained variability from both short timescale (days) dimming events, and years-long fading in the Kepler mission. No single physical mechanism has successfully explained these observations to date. Here we investigate the ultraviolet variability of KIC 8462852 on a range of timescales using data from the GALEX mission that occurred contemporaneously with the Kepler mission. The wide wavelength baseline between the Kepler and GALEX data provides a unique constraint on the nature of the variability. Using 1600 s of photon-counting data from four GALEX visits spread over 70 days in 2011, we find no coherent NUV variability in the system on 10--100 s or month timescales. Comparing the integrated flux from these 2011 visits to the 2012 NUV flux published in the GALEX-CAUSE Kepler survey, we find a 3% decrease in brightness for KIC 8462852. We find that this level of variability is significant, but not necessarily unusual for stars of similar spectral type in the GALEX data. This decrease coincides with the secular optical fading reported by Montet & Simon. We find that the multi-wavelength variability is somewhat inconsistent with typical interstellar dust absorption, but instead favors a {R}V=5.0+/- 0.9 reddening law potentially from circumstellar dust.

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Non-grey dimming events of KIC 8462852 from GTC spectrophotometry

Deeg, Hans J.; Alonso, Roi; Nespral, David; Boyajian, Tabetha S.
02/2018

We report ground-based spectrophotometry of KIC 8462852 obtained during its first dimming events since the end of the Kepler mission. The dimmings show a clear colour signature and are deeper in visual blue than in red wavelengths. The wavelength dependency of the flux loss can be described with an absorption Ångström coefficient of 2.19 ± 0.45, which is compatible with absorption by optically thin dust with particle sizes of the order of 0.0015 to 0.15 mum. These particles would be smaller than is required to be resistant against blow-out by radiation pressure when close to the star. During occultation events, these particles must be replenished from a comoving body on time-scales of days. If dust is indeed the source of the dimming events of KIC 8462852, deeper dimming events should show more neutral colours, as is expected from optically thick absorbers.

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KIC 8462852: Will the Trojans return in 2021?

Ballesteros, Fernando J.; Arnalte-Mur, Pablo; Fernandez-Soto, Alberto; Martínez, Vicent J.
01/2018

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, asymmetric dimming taking up to 15 per cent of the light at D793 and a period of multiple, narrow dimmings happening approximately 700 d 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 yr, 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.

8. One of my takeaways from the above is that a model of what is going on with this star can be put together in the near future (to 2023 or so) if certain events are repeated. Lots of fascinating speculation.

9. Originally Posted by CJSF
Maybe it's more telling of the human(s) making the doomsday statements than of any purported aliens.
I accept that.

10. Originally Posted by Roger E. Moore
What we don't know could kill us.
(it was easier to quote the shorter post)

We're getting off topic, but I think the idea that aliens are going to come to Earth and harm us in some way is so remote that it doesn't even make the list of things to even think about.

We are doing quite a fine job of killing ourselves and our planet; there is no need to evoke some outside cause of that.

11. UPDATED DATA

https://arxiv.org/abs/1710.01081

A 1574-day periodicity of transits orbiting KIC 8462852

Gary Sacco, Linh Ngo, Julien Modolo
(Submitted on 3 Oct 2017 (v1), last revised 3 Aug 2018 (this version, v4))

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.

12. https://arxiv.org/abs/1712.06637

Reddened Dimming of Boyajian's Star Supports Internal Storage of Its "Missing" Flux

Peter Foukal
(Submitted on 12 Dec 2017)

Two recent short term dimmings of KIC 8462852 (Boyajian's Star) exhibit clear reddening in the B, r' and i' photometric passbands. We show that the intensity ratios of the three pass bands agree well with cooling of an approximately 6800 K black body by about 30K. This agreement, together with other recent findings on the timing and longer term dimmings of this star, support our previous argument that the star's photometric behavior is caused by internal storage of impeded convective flux, rather than by external sources of obscuration such the ISM or circumstellar material.

13. Would there be any similarity, at least in outward appearance if not in actual nature, between this star and KIC 8462852? Just curious.

https://arxiv.org/abs/1712.08962

Is the Young Star RZ Piscium Consuming Its Own (Planetary) Offspring?

K. M. Punzi, J. H. Kastner, C. Melis, B. Zuckerman, C. Pilachowski, L. Gingerich, T. Knapp
(Submitted on 24 Dec 2017)

The erratically variable star RZ Piscium (RZ Psc) displays extreme optical dropout events and strikingly large excess infrared emission. To ascertain the evolutionary status of this intriguing star, we obtained observations of RZ Psc with the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton), as well as high-resolution optical spectroscopy with the Hamilton Echelle on the Lick Shane 3 m telescope and with HIRES on the Keck I 10 m telescope. The optical spectroscopy data demonstrate that RZ Psc is a pre-main sequence star with an effective temperature of 5600 ± 75 K and log g of 4.35 ± 0.10. The ratio of X-ray to bolometric luminosity, log L X /L bol , lies in the range -3.7 to -3.2, consistent with ratios typical of young, solar-mass stars, thereby providing strong support for the young star status of RZ Psc. The Li absorption line strength of RZ Psc suggests an age in the range 30-50 Myr, which in turn implies that RZ Psc lies at a distance of ∼ 170 pc. Adopting this estimated distance, we find the Galactic space velocity of RZ Psc to be similar to the space velocities of stars in young moving groups near the Sun. Optical spectral features indicative of activity and/or circumstellar material are present in our spectra over multiple epochs, which provide evidence for the presence of a significant mass of circumstellar gas associated with RZ Psc. We suggest that the destruction of one or more massive orbiting bodies has recently occurred within 1 au of the star, and we are viewing the aftermath of such an event along the plane of the orbiting debris.

14. https://arxiv.org/abs/1809.00693

A Reassessment of Families of Solutions to the Puzzle of Boyajian's Star

Jason T. Wright
(Submitted on 3 Sep 2018)

Wright & Sigurdsson (2016) described several families of plausible solutions to the puzzle of Boyajian's Star (Boyajian et al. 2016), and ranked some of them by their subjective plausibility. Since then, theoretical and observational work have altered many families' plausibility, and so in this Research Note I reassess them, including the possibilities of intrinsic variation, intervening ISM or circum-black hole material, and circumstellar material such as exocomets.

[[SPOILERS! -- REM]]

REASSESSED FAMILIES OF SOLUTIONS: Instrumental effects are now not worth any consideration: instruments other than Kepler have seen the dips. Pulsations are less likely now because of the constancy of in-dip RVs. Explanations involving only opaque objects such as stars, planets, swarms of asteroids, or alien megastructures (Wright et al. 2016) are now ruled out.

Polar spots continue to be unlikely. The Solar System cloud model still needs development (but see Katz 2017).

All models involving interstellar dust are supported by the dips’ colors, but now must grapple with the lack of increased gas column during dips. This is not necessarily a fatal problem: on the very small length scales required to produce the dips, dust and gas in the ISM may be uncoupled. Further, the ISM sodium absorption lines are saturated and so are relatively insensitive to additional neutral gas at the same RV as the known clouds. The calcium lines do not appear to be saturated, but might not be expected to trace the dust well, anyway.

The post-merger return to normal hypothesis is now plausible thanks to the work of Metzger et al. (2017), but still requires development to predict the color and spectral changes one expects to see, as well as an explanation for the secular brightening.

Intrinsic variability now has some theoretical support (Foukal 2017a), and appears to be consistent with the multi-band photometry (Sheikh et al. 2016; Foukal 2017b; Boyajian et al. 2018), although a mechanism and explanation for its rarity remain elusive (but see Lacki 2016). It is also consistent with the lack of significant additional gas absorption during a dip.

The measured reddening may favor circumstellar material, and thus moves this family of solutions up in plausibility, however these models still struggle with the lack of observed NIR excess and the short lifetime implied by the small dust grains found by Boyajian et al. (2018) and Deeg et al. (2018). Additionally, the lack of gas accompanying the very fine dust would seem to argue against an “exocometary” origin for the dust. A quantitative calculation of the amount of gas and the dust replenishment rate in these scenarios would be helpful. It may be more likely that the material is produced collisionally from “dry” asteroids at large distances from the star.

Finally, the Wright & Sigurdsson (2016) hypothesis of an intervening black hole disk appears to still be in play, and should be investigated. In particular, such dust might be characteristic of circumstellar grains, and the lack of accompanying gas could be due to the unusual abundance patterns of such a disk, or it could be so cold that all of its gas has condensed onto grains. The dust in this hypothesis is far from any source of strong, radiation and so is consistent with the continued lack of IR excess, and the persistence of the dust despite its small typical grain size.

15. My Stupid Opinion: I was surprised the black-hole option was considered viable, as it seemed there should be other signs indicating a black hole was present (but none are reported).

16. http://www.wherestheflux.com/blog

The link goes to "Where's the Flux?", the official website for Boyajian's Star. The blog is shown first here, with data for September 2018 now up.

17. Another Tabby's Star? Hold on to your butts.

VVV-WIT-07: another Boyajian's star or a Mamajek's object?

Roberto K. Saito, et al. (Submitted on 6 Nov 2018)

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 Variables in the Vía Láctea (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, alternatively, 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.

18. Here we go again. More on VVV-WIT-07...

https://www.sciencenews.org/article/...by-star?tgt=nr

Astronomers spot another star that flickers like Tabby’s star
It’s unclear what’s causing the newly discovered object to blink, but it’s probably not aliens

By Lisa Grossman : 10:14am, November 16, 2018

QUOTE: The researchers had been searching for supernovas, stars that suddenly brighten as they explode, when the team spotted the object in data taken with the VISTA telescope in the Atacama Desert in northern Chile. The data were part of a larger survey of the galaxy’s center called the VISTA Variables in the Vía Láctea, or VVV.

Instead of brightening, this star suddenly dimmed. The team called it VVV-WIT-07, for “What is this?” From 2010 to 2018, the star’s brightness waxed and waned with no set pattern. That lack of pattern is similar to Tabby’s star, except VVV-WIT-07’s light dropped by up to 80 percent, while Tabby’s star dimmed by only about 20 percent.

There’s another flickering star, J1407, that might be a closer match. That star periodically dims by up to 95 percent, astronomer Eric Mamajek of the University of Rochester in New York and colleagues reported in 2012. Astronomers think J1407 hosts an orbiting planet with an enormous ring system that periodically eclipses the star (SN: 3/7/15, p. 5).

Finding multiple stars that all dim sporadically could mean that the sources of such flickering, whatever they are, must be relatively routine, says astronomer Tabetha Boyajian of Louisiana State University in Baton Rouge, who is also Tabby’s star’s namesake. “If this phenomenon is the same as what’s happening with Tabby’s star, then we can’t invoke an elaborate explanation for what’s happening in both systems,” Boyajian says. “If you’re starting to see stars similar to this all over the place, then it’s got to be a really common thing that happens in nature. That’s really cool.”

19. Looking less like its was aliens and more like it was regular (?) stuff.

https://arxiv.org/abs/1812.06837

High-resolution spectroscopy of Boyajian's star during optical dimming events

M. J. Martínez González, et al. (Submitted on 17 Dec 2018)

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 exocomets 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.

QUOTES: We do not detect any signature in the photospheric average line that is modulated by rotation (assuming the 0.88 day period). This non-detection at our noise level, together with the modulation of the light curve observed by Kepler, imposes an upper limit to the cold spots that could be present at the surface of the star. We estimate that possible spots in the star occupy, at most, 0.002% of the surface, a factor ten times larger than typical solar spots. Though spots have not been detected in the tomography, we still nd them to be the most plausible explanation for the modulation of the light curve with a 0.88 day period detected by Kepler.

Some of the hypotheses found in the literature concerning the dimmings of the star are related to clouds of interstellar material or falling evaporating bodies (also referred as exocomets). Our spectroscopic survey does not strengthen either of the two scenarios. The spectral lines of the interstellar medium gas do not change during the dimmings. However, since we do not detect spectral signatures of the dust, we can not discard the interstellar dust as the star's occulter. At our sensitivity, we do not detect any absorption signature in the Ca ii H and K lines due to exocometary tails.

We compute the radial velocities of the average photospheric line in all our spectra. We detect, at a 1-2 sigma level, a drop in the radial velocity of the star during the Elsie event. Since it has been shown that the dimming events are chromatic and likely due to optically thin dust (Boyajian et al. 2018), we claim that the dusty environment around the Boyajian's star has some clumps of thick material (with likely inclined and high impact parameter orbits) that produce the Rossiter-McLaughlin effect. However, since it is only a 1-2 sigma detection, we encourage future spectroscopic follow-up to strengthen or reject this scenario.

20. However, there are still those looking for aliens.

https://arxiv.org/abs/1812.10161

The Breakthrough Listen Search for Intelligent Life: Searching Boyajian's Star for Laser Line Emission

David Lipman, et al. (Submitted on 25 Dec 2018)

Boyajian's Star (KIC 8462852) has received significant attention due to its unusual periodic brightness fluctuations detected by the Kepler Spacecraft and subsequent ground based observations. Possible explanations for the dips in the photometric measurements include interstellar or circumstellar dust, and it has been speculated that an artificial megastructure could be responsible. We analyze 177 high-resolution spectra of Boyajian's Star in an effort to detect potential laser signals from extraterrestrial civilizations. The spectra were obtained by the Lick Observatory's Automated Planet Finder telescope as part of the Breakthrough Listen Project, and cover the wavelength range of visible light from 374 to 970 nm. We calculate that the APF would be capable of detecting lasers of power greater than approximately 24 MW at the distance of Boyajian's Star, d = 1470 ly. The top candidates from the analysis can all be explained as either cosmic ray hits, stellar emission lines or atmospheric air glow emission lines.

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