Open AccessThe APM survey for cool carbon stars in the Galactic halo – I
Author(s) -
E. J. Totten,
M. J. Irwin
Publication year - 1998
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1998.01086.x
Subject(s) - physics , astrophysics , carbon star , galactic halo , astronomy , stars , halo , galaxy , milky way , sky
A by‐product of the APM high‐redshift quasar survey was the discovery of several distant (20–100 kpc) N‐type carbon stars at high galactic latitude. Following on from this, we have started a systematic all‐sky survey at galactic latitudes ⊢ b ⊢>30° to find further examples of these rare objects, and we report here on the results from the first season of follow‐up spectroscopy. Faint, high‐latitude carbon (FHLC) giants make excellent probes of the kinematic structure of the outer Galactic halo. Therefore, in addition to detailed spectrophotometry covering a wide wavelength range, we have obtained high‐resolution (∼1 Å) spectra centred on the CN bands at ∼8000 Å, and have derived accurate (≲10 km s −1 ) radial velocities for the known FHLC stars. From the initial phase of our survey covering ≈6500 deg 2 , we find a surface density of faint N‐type carbon stars in the halo of ≈1 per 200 deg 2 , roughly a factor of 4 less than the surface density of CH‐type carbon stars in the halo. Intermediate‐age, N‐type carbon stars seem unlikely to have formed in the halo in isolation from other star‐forming regions, and one possibility that we are investigating is that they either arise from the disruption of tidally captured dwarf satellite galaxies or are a manifestation of the long‐sought optical component of the Magellanic Stream.