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Caleb Abbott F-Stars a Not-Unexpected Journey

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Caleb Abbott F-Stars a Not-Unexpected Journey CALEB ABBOTT F-STARS A NOT-UNEXPECTED JOURNEY ▸ What the F-stars are? ▸ Optical Classification: ▸ Thermal ▸ Luminosity ▸ Peculiar F-Type Stars ▸� Puppis Stars ▸Barium Dwarfs ▸High Latitude F Supergiants ▸WTF Star? WHAT IS IT, PRECIOUS? ▸ About 1 in 33 MS stars in our neighborhood are F-type stars. ▸ Mass: 1 - 1.4 Msun ▸ Temperatures: 6,000 - 7,600 K ▸ Important range for physical TOSS IT INTO THE FIRE! changes in the atmosphere… ▸ CONVECTION! THE BOARD IS SET… ▸ Optical Classification: ▸ Temperature Criteria! ▸ Using Hydrogen line strength and profiles: ▸ Least affected by metallicity ▸ Can be used to determine, within one subtype, the Temperature of the F-Star ▸ Metal Lines are secondary criteria ▸ Ca II K line ▸ Not very useful after F3 ▸ Relations of Fe and Ca to H lines can get T for F5 stars on MS ▸ Late Am stars with H lines are typed, rarely, as F2 (see � Puppis stars) THE PIECES ARE MOVING ▸ Luminosity Criteria ▸ Pre F6-stars, the primary criteria are ionized Fe and Ti lines ▸ See “forest” near 4500 Å ▸ Max sensitivity between F0 and F2 ▸ For F8 stars the Ca II K and H lines show mild positive luminosity effect. ▸ Broadening THE PECULIAR (AKA COOL) SO MUCH FEAR AND DOUBT, OVER SO SMALL A THING ▸ � Puppis ▸ Unusually late, probably evolved Am-type stars ▸ Gray reclassified many of these bright objects (originally called ẟ Delphini — Del— Stars) and found four main groups ▸ Essentially normal, low rotational velocities ▸ Essentially normal, minor strengthen of metallic-line spectrum ▸ proto-Am stars ▸ The legit � Puppis stars! � PUPPIS, NEVER HEARD OF � PUPPIS BEFORE ▸ � Puppis, θ Gru, HD 103877, and possibly � Uma ▸ Appear to be late Am stars ▸ H line types are F5 ▸ Lum. types range from II- III to Ib RETURN OF THE KING � PUPPIS ▸ A ẟ Scuti pulsator with large amplitude ▸ Odd due to the case of helium having settled in Am atmospheres, resulting in no helium convection zone ▸ Not the case for � Puppis ▸ Engine for pulsations relates to helium ionization in convection zone ▸ As � Puppis left the MS, it developed deep convection zones as it expanded and cooled from Am star A COMPANY OF DWARFS ▸ Barium dwarfs ▸ Does not actually have a very enhanced Ba II 4554 Å line… ▸ But does have exceptionally strong Sr II (4077 and 4216 Å) lines ▸ Slightly metal weak ▸ Unusual because of convection?!? ▸ Ba and Sr produced primarily through s-process in cores of stars on the AGB ▸ Can be mixed to the surface by deep convection ▸ But this is not possible in dwarf stars?!? ▸ The answer is… BINARIES!!!! ▸ The discovery of barium giants! ▸ IN BINARIES! ▸ WD companions ▸ Roche lobe interaction/wind accretion to contaminate the dwarf ▸ Matches observations! ▸ Radial velocity variations ▸ However, no companions have been detected RR-LYRAE ▸ Lame HIGH-LATITUDE F SUPERGIANTS ▸ A few F-type supergiants appear either (essentially) normal or are metal weak and are found at high latitudes ▸ Many have high velocities ▸ Thick disk or halo ▸ HD 46703 has enhanced carbon abundance ▸ The three sample stars resemble MK A5 superficially ▸ Differing H lines, much stronger in A5 Ib ▸ What is the origin of these stars? ▸ Are these high mass supergiants that happen to be at high latitude, or are they low mass stars “masquerading” as high mass supergiants? HIGH MASS SUPERGIANTS ▸ If so, could have been ejected from the plane, perhaps from binary systems/disturbances ▸ Supported by many being high velocity stars ▸ Or maybe they were born above the plane? OR THEY’RE PHONIES… ▸ They could be low mass Pop II stars in post AGB phase ▸ Many show IR excess ▸ HD 46703 has overabundance of C, N, O, and S but is metal weak ▸ CNO abundance suggest H and He burning have been dredged to surface ▸ S abundance may be due to alpha capture during core helium flash ▸ These suggest this (HD 46703) is a post AGB star. WTF STAR ▸ Where’s the flux…also known as the Tabby’s star ▸ Very unusual light curve ▸ Small, but frequent, non-periodic dips in brightness ▸ The change is consistent with many small masses in “tight formation” THE BIG DIP ▸ First dip (March 5th, 2011) obscured 15% of the star’s brightness ▸ Second dip (February 28th, 2013) obscured 22% ▸ 750 day cycle? ▸ Due to technical reasons, could not be observed February, 2015 ▸ Future observations planned for May, 2017 HISTORY ▸ Photographic plates suggest star has dimmed, gradually, from 1890 to 1989, by about 20% ▸ Kepler found it dimmed 0.34% per year (with a big dip of 2.4% over 200 days) ▸ No other nearby stars have similar behavior WHAT THE FLUX IS GOING ON? ▸ Young star with accretion disk? ▸ No evidence within a few AU :( WHAT THE FLUX IS GOING ON? ▸ Planetary debris field? ▸ No IR excess from post-impact leftover dust ▸ Planetary interactions unlikely to begin with? ▸ No spectroscopic evidence within a few AU WHAT THE FLUX IS GOING ON? ▸ Cloud of disintegrating comets? ▸ Assumes star has Oort cloud- like structure ▸ Gravity from nearby star causes comets to fall closer in ▸ There is a nearby M red dwarf (885 AU away) ▸ How many comets to reduce brightness 22%? WHAT THE FLUX IS GOING ON? ▸ Consumption of Planet? ▸ Swallowing planet causes temporary, but unobservable, increase in brightness due to release of gravitational energy ▸ Remaining orbiting debris (disk) could explain drops in intensity? WHAT THE FLUX IS GOING ON? ▸ DYSON SPHERE/SWARM!!!! ▸ Advanced life! ▸ SETI has yet to find anything.
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