Showing papers by "Mike Irwin published in 1993"

Discovery of a Third Giant Low Surface Brightness Disk Galaxy

Abstract: We report the discovery of a third very large, gas-rich low surface brightness (LSB) disk galaxy, which we designate 1226+0105. Its equatorial coordinates are α=12 h 26 m 39 s .2 and δ=1°05'38″ (1950), and it is at a redshift of 23,660 km s −1 . It exhibits a number of similarities to the previous described examples of this class, Malin 1 (Bothun et al. 1987; Impey & Bothun 1989) and F568-6 (Bothun et al. 1990), in that it has a large total H I mass of ∼2×10 10 M ○. , a long disk scale length of ∼14 kpc, a high total luminosity of M B =−21.6, and it harbors an active nucleus. It also shows some striking differences from the previous two

Very red stars between the Magellanic Clouds: discovery of carbon stars in the outer LMC and SMC haloes

Abstract: We present a list of 57 very red stars, B−V>1.75, selected from ∼5×10 5 stars in three UK Schmidt fields between the Magellanic Clouds. These stars have an apparent magnitude distribution compatible with LMC carbon stars. They are located between 5° and 15° from the centre of the LMC. Follow-up spectroscopy of most of the candidates shows that more than two-thirds of them are indeed carbon stars. These red stars should be useful to establish better the dynamics of the outer haloes of the Magellanic Clouds

Deep CCD photometry of the dwarf spheroidal galaxy Leo I.

Abstract: We present a deep colour-magnitude diagram of the central 7×7 arcmin 2 region of Leo II The diagram shows a well-defined giant branch and a red horizontal branch, heavily populated on the red side but extending far into the blue Having a low metallicity [Fe/H]=−19), the Leo II diagram is similar to those of outer halo clusters suffering from the second-parameter syndrome From the mean apparent magnitude of candidate RR Lyrae stars, =2210, we estimate the distance of Leo II to be 215 kpc, a value similar to previous estimates A number of variable-star candidates are identified and two new very red giants have been found Comparison with the other dwarf spheroidals of the Local Group reveals that Leo II belongs to the group of four small and faint dwarf speroidal galaxies

More dwarf carbon stars

Abstract: We have discovered three very faint carbon stars (m V >19) in the course of a multicolour survey for high-redshift quasars. Proper motion measurements have been made of these stars to determine their luminosity class. On this basis, the star 0045-259 is confirmed as a halo dwarf, joining the four dwarf carbon stars already known. These five dwarfs appear to have similar absolute magnitudes and tangential velocities. A second star, 0041 - 295, is also a dwarf, yet either its absolute magnitude or its tangential velocity differs from those of the five other dwarfs; it may be the first disc dwarf carbon star found. The time baseline for the proper motion measurement for the third star, 2048-48, is too small to allow the luminosity class to be determined

The absolute proper motion and Galactic orbit of M3

Abstract: The combination of Schmidt plates and an automatic measuring machine provides a powerful method for investigating the proper motions of both the Galactic halo globular clusters and the nearby Galactic dwarf spheroidal satellites. We describe the first direct measurement of the absolute proper motion of a Galactic globular cluster with respect to a large number of background galaxies. Five pairs of Tautenburg Schmidt plates centred on the cluster M3, with epoch differences from 20 to 23 yr, were scanned using the automatic plate measuring facility in Cambridge. The proper motion determination was based on a stepwise regression method with generalized third-order polynomials and used between 1200 and 2200 galaxies for each pair of plates to define an inertial reference frame

The detection of an extended moving group near the galactic disk

Abstract: A radial velocity survey (median velocity precision ∼1.0 km s −1 ) for 879 field stars in the direction (l, b)=(277°, 9°) has been undertaken with the bench-mounted spectrograph, ARGUS, and echelle grating at the CTIO 4.0 m telescope. The radial velocity histogram shows a marked overabundance of stars in the range 74,0-76.0 km s −1 . We observe 18 stars in this interval, whereas only five such stars (within our ∼1° field) are expected on the basis of the Institute for Advanced Study Galaxy Model. Monte Carlo simulations indicate that this feature is significant at better than the 99% level

The Hot DAB Degenerates in the MCT Survey

Abstract: The DAB white dwarfs represent a class of hybrid white dwarfs where weak neutral helium lines are superposed onto the classical hydrogen-line spectrum of DA stars. Such stars are rare: until recently the only known DAB star was the prototype GD 323, discovered independently by Oke, Weidemann, & Koester (1984) and Liebert et al. (1984). More recently, a second DAB star, G104-27, was discussed by Holberg, Kidder, & Wesemael (1990), but the exact nature of this object still remains unclear as the weak He I lines reported earlier have not been detected in the subsequent observations of Kidder et al. (1992).