CALEB ABBOTT F- A NOT-UNEXPECTED JOURNEY

▸ What the F-stars are?

▸ Optical Classification:

▸ Thermal

▸

▸ Peculiar F-Type Stars

▸� Stars

▸Barium Dwarfs

▸High Latitude F Supergiants

▸WTF ? 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

▸ 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!

▸ 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 (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