arXiv subjects

M. J. Currie

Publications and source records attributed to M. J. Currie.

24 records · Page 2Linked to original sources

arXiv2008

A critical review of the evidence for M32 being a compact dwarf satellite of M31 rather than a more distant normal galaxy

Since Baade's photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope (HST) based stellar population studies which have resolved red-giant branch (RGB) and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32's anomalously high central velocity dispersion for a dwarf galaxy (several times that of either NGC 147, NGC 185 or NGC 205) or existing planetary nebula observations (which suggest that M32 is more than twice as distant as M31) and also requires an elaborate physical explanation for M32's inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by: (1) a central velocity dispersion typical of intermediate galaxies, (2) the published planetary nebula observations, and (3) known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary. This suggests that current understanding of some relevant fields is still very far from adequate.

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arXiv2006

WFCAM, Spitzer-IRAC and SCUBA observations of the massive star forming region DR21/W75: I. The collimated molecular jets

We present wide-field near-infrared images of the DR21/W75 high-mass star forming region, obtained with the Wide Field Camera, WFCAM, on the United Kingdom Infrared Telescope. Broad-band JHK and narrow-band H2 1-0S(1) images are compared to archival mid-IR images from the Spitzer Space Telescope, and 850 micron dust-continuum maps obtained with the Submillimeter Common User Bolometer Array (SCUBA). Together these data give a complete picture of dynamic star formation across this extensive region, which includes at least four separate star forming sites in various stages of evolution. The H2 data reveal knots and bow shocks associated with more than 50 individual flows. Most are well collimated, and at least five qualify as parsec-scale flows. Most appear to be driven by embedded, low-mass protostars. The orientations of the outflows, particularly from the few higher-mass sources in the region (DR21, DR21(OH), W75N and ERO~1), show some degree of order, being preferentially orientated roughly orthogonal to the chain of dusty cores that runs north-south through DR21. Clustering may inhibit disk accretion and therefore the production of outflows; we certainly do not see enhanced outflow activity from clusters of protostars. Finally, although the low-mass protostellar outflows are abundant and widely distributed, the current generation does not provide sufficient momentum and kinetic energy to account for the observed turbulent motions in the DR21/W75 giant molecular clouds. Rather, multiple epochs of outflow activity are required over the million-year timescale for turbulent decay.

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arXiv2006

JHK Observations of Faint Standard Stars in the Mauna Kea Near-Infrared Photometric System

JHK photometry in the Mauna Kea Observatory (MKO) near-IR system is presented for 115 stars. Of these, 79 are UKIRT standards and 42 are LCO standards. The average brightness is 11.5 mag, with a range of 10 to 15. The average number of nights each star was observed is 4, and the average of the internal error of the final results is 0.011 mag. These JHK data agree with those reported by other groups to 0.02 mag. The measurements are used to derive transformations between the MKO JHK photometric system and the UKIRT, LCO and 2MASS systems. The 2MASS-MKO data scatter by 0.05 mag for redder stars: 2MASS-J includes H2O features in dwarfs and MKO-K includes CO features in giants. Transformations derived for stars whose spectra contain only weak features cannot give accurate transformations for objects with strong absorption features within a filter bandpasses. We find evidence of systematic effects at the 0.02 mag level in the photometry of stars with J<11 and H,K<10.5. This is due to an underestimate of the linearity correction for stars observed with the shortest exposure times; very accurate photometry of stars approaching the saturation limits of infrared detectors which are operated in double-read mode is difficult to obtain. Four stars in the sample, GSPC S705-D, FS 116 (B216-b7), FS 144 (Ser-EC84) and FS 32 (Feige 108), may be variable. 84 stars in the sample have 11< J< 15 and 10.5<H,K<15, are not suspected to be variable, and have magnitudes with an estimated error <0.027 mag; 79 of these have an error of <0.020 mag. These represent the first published high-accuracy JHK stellar photometry in the MKO photometric system; we recommend these objects be employed as primary standards for that system [abridged].

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arXiv2005

On the Interpretation of High Velocity White Dwarfs as Members of the Galactic Halo

A detailed analysis of 32 of the 38 halo white dwarf candidates identified by Oppenheimer et al. is presented, based on model atmosphere fits to observed energy distributions built from optical BVRI and infrared JHK CCD photometry. Effective temperatures and atmospheric compositions are determined for all objects, as well as masses and cooling ages when trigonometric parallax measurements are available. This sample is combined with that of other halo white dwarf candidates and disk white dwarfs to study the nature of these objects in terms of reduced proper motion diagrams, tangential velocities, and stellar ages. We reaffirm the conclusions of an earlier analysis based on photographic magnitudes of the same sample that total stellar ages must be derived in order to associate a white dwarf with the old halo population, and that this can only be accomplished through precise mass and distance determinations.

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arXiv2003

L' and M' Standard Stars for the Mauna Kea Observatories Near-Infrared System

We present L'and M' photometry, obtained at UKIRT using the Mauna Kea Observatories Near-IR filter set, for 46 and 31 standard stars, respectively. The L' standards include 25 from the UKIRT in-house "Bright Standards" with magnitudes deriving from Elias et al. (1982) and observations at the IRTF in the early 1980s, and 21 fainter stars. The M' magnitudes derive from the results of Sinton & Tittemore (1984). We estimate the average external error to be 0.015 mag for the bright L' standards and 0.025 mag for the fainter L' standards, and 0.026 mag for the M' standards. The new results provide a network of homogeneously observed standards, and establish reference stars for the MKO system, in these bands. They also extend the available standards to magnitudes which should be faint enough to be accessible for observations with modern detectors on large and very large telescopes.

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arXiv1998

Distance indicators based on the luminosity-profile shapes of early-type galaxies--a reply

In a recent paper, Binggeli & Jerjen (1998) question the value of the extra- galactic distance indicators presented by Young & Currie (1994 & 1995) and state that they have refuted `the claim that the Virgo dEs [dwarf-elliptical galaxies]...are distributed in a prolate structure stretching from 8 to 20 Mpc distance (Young & Currie 1995).' even though no such claim was ever made. In this paper, we examine Binggeli & Jerjen's claims that intrinsic scatter rather than spatial depth must be the main cause of the large scatters observed in the relevant scaling relationships for Virgo galaxies. We investigate the accuracy of Binggeli & Jerjen's photometric parameters and find that while their profile curvature and scalelength measurements are probably useful, their total magnitude and central surface-brightness measurements are not useful for the purpose of investigating scaling laws because they suffer from serious systematic and random errors. We also investigate Binggeli & Jerjen's criti- cisms of our (1995) analysis. We demonstrate that their test for strong mutual dependence between distance estimates based on the two different scaling laws is invalid because of its prior assumption of negligible cluster depth. We further demonstrate that the [relative] distance estimates on which their kinematical arguments are based cannot be meaningful, not only because of the seriousness of the photometric errors, but also because they are undermined by the prior assumption that depth effects can again be neglected.

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