Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20921908g&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #219.08; Bulletin of the American Astronomical Society,
Astronomy and Astrophysics
Astronomy
Scientific paper
Interferometric studies of bright stars have demonstrated that some of the best studied A stars are rapid rotators which have 2000K latitudinal gradients in T_eff. This large temperature gradient has two important consequences: at A5 or later, such stars can support convection and may have enhanced activity and having depressed UV and FUV fluxes compared to slowly rotating stars. Both of these phenomena have implications for the evolution of protoplanetary disks and the habitability of young planets in such systems. Combining inclinations and v sin i data permits us to identify the rapid rotators among systems which are still accreting and with central disk clearing. For two near-ZAMS Herbig Ae/Fe stars, HD 169142 and HD 135344 with v>235 km/s we find both enhanced x-ray activity and emission in chromospheric and transition region species compared to more typically rotating mid-A and F members of the Beta Pictoris Moving Group (BPMG). Both stars have IR SEDs suggesting that the outer disks are relatively flat. To avoid shadowing of the outer disk under these circumstances, the inner disks are either geometrically thin or are partially devoid of material. The FUV data for HD 135344 are consistent with stellar activity without accretion, while HD 169142 has an X-ray pulse-height spectrum similar to non-accreting early F members of the BPMG. The inner disks in both systems are too large to have been produced by photo-evaporation alone, suggesting the presence of second bodies in the inner disk. For HD 169142, the X-ray spectrum is very soft, unlike young, low-mass stars, and suggesting in tandem with the brown dwarf desert within 100 AU of the star these systems may harbor gas-giant planets.
Carpenter W.
Collins Karen
Grady Carol A.
Hamaguchi Kenji
Henning Th
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