Dennis R. Crabtree

Late-Type Stars in M31. I. Photometric Study of AGB Stars and Metallicity Gradients

We have imaged five 7\arcmin \x 7\arcmin\ fields in M31 spanning galactocentric radii from 4 to 32 kpc along the SW-major axis. The fields were observed through two broad-band (\V\ and \I) and two narrow-band (\CN\ and \TiO) filters. The broad-band data were used to construct \IvsVI\ color-magnitude diagrams (CMDs) and, in some of our fields, we found significant numbers of stars in the Cepheid instability strip. A distance modulus for the Cepheids in the middle field was found that agreed well with other values in the literature values. The width of the giant branch (GB) in the \IvsVI\ CMD of all 5 fields was investigated, and we show that in four of the fields a likely explanation for the GB width is a combination of {\it both} metallicity and mass variations. Using the broad-band data, the asymptotic giant branch (AGB) luminosity functions (LFs) were measured in the five fields, and we show that differences exist between these LFs. We speculate on how the different star forming histories in the fields may lead to the observed AGB LFs and GB widths. Using the narrow-band data along with the broad-band data we separated the AGB stars into carbon-rich (C) and oxygen-rich (M) types. The carbon stars LFs were used to obtain an estimate for the distance modulus of M31 which agrees with the value derived from Cepheids. The ratio of C- to M-stars (C/M) is believed to be an indicator of gaseous chemical abundance at the time of formation of these stars. We show that the C/M ratio increases smoothly with galactocentric distance, suggesting an inverse correlation with metallicity. This is the first demonstration of this effect within a single extragalactic system. We find that differences in the width of the GB and the AGB LFs do not significantly affect the C/M ratio. We consider the effect of the increasing C/M ratio on the ISM in M31, and cite evidence in favor of a model where the grain composition in M31 is a function of galactocentric distance.

Star and cluster formation in NGC 1275

Imaging of the nuclear region of the central galaxy in the Perseus Cluster, NGC 1275, has confirmed the existence of luminous, blue, and unresolved objects surrounding the nucleus. A search of archival material indicates that none of these objects has varied significantly over the past 8 yr and that no new bright objects have either appeared or disappeared. This eliminates either ultraluminous stars or supernovae as explanations of these sources; young and luminous star clusters are the most probable interpretation. Analysis of the photometry of these clusters suggests that they have formed continuously at least over the past several hundred million years, making it unlikely that a galaxy-galaxy interaction triggered the star formation

The late-type stellar content of NGC 2403

The late-type stellar content of three disk fields in NGC 2403 was examined using Cousins RI and VI CCD photometry. The AGB luminosity function has been constructed separately for the inner and outer fields. In both cases, relatively fewer bright AGB stars are seen in the NGC 2403 fields than in the LMC. The shape of the AGB luminosity function for the innermost field is quite different from that of the LMC, and there is an indication that recent star formation may have occurred. Several red and blue supergiants and H II regions are also identified in the field to support this. The luminosity function for the outer NGC 2403 fields appears more similar to that of the LMC, and a difference in the star-formation rate in the two regions of NGC 2403 is suggested. A narrowband photometric technique has been used to identify carbon and M stars in the innermost field. Several late M stars are identified, but the carbon star identifications are, at best, tentative. 38 refs.

Late-type stars in an inner and far disk field of M31

Two disk fields in M31, one in Baades field IV at 20 kpc from the nucleus of the galaxy and the other at 4 kpc, were surveyed for late-type stars using broad-band V and I filters (both fields) as well as narrow-band filters in the outer field. The carbon to late M star ratio in the outer field was found to be 0.15, almost identical to that in a field at 11 kpc studied earlier. The CM diagram for the outer field clearly shows a giant branch which extends well to the red of that of the most metal-rich globular cluster. The carbon stars occupy a relatively unique position in this diagram, being in general the most luminous objects in the field. The widths of the giant branches in both fiels are much wider than can be accounted for by photometric errors. The distance to M31 is also determined using the carbon stars. A true distance modulus of 24.45 is found. 33 refs.

Scientific productivity and impact of large telescopes

The primary scientific output from an astronomical telescope is the collection of papers published in refereed journals. A telescopes productivity is measured by the number of papers published which are based upon data taken with the telescope. The scientific impact of a paper can be measured quantitatively by the number of citations that the paper receives. In this paper I will examine the productivity and impact of the CFHT, Gemini, Keck, Magellan, Subaru, UKIRT and VLT telescopes using paper and citation counts.

Canadian very large optical telescope technical studies

A design is proposed for a 20 m Canadian Very Large Optical Telescope (VLOT). This design meets the science, schedule, and availability requirements of the Canadian astronomical community. The telescope could be operational by early in the next decade to complement the science discoveries of the Next Generation Space Telescope (NGST) and Atacama Large Millimeter Array (ALMA). This design is suitable for location on the Mauna Kea summit ridge, and could replace the current 3.6 m CFHT telescope. The telescope structure provides room for two vertically oriented Nasmyth instruments, implements a very stiff monocoque mirror cell, and offers a short and direct load path to the telescope mount. A Calotte style dome structure offers many advantages over current designs including lower and more even power requirements, and a circular aperture that will better protect the telescope structure from wind buffeting. The science requirements are presented, and the telescope optical design, primary mirror pupil segmentation options, including hexagonal segments and a radial segment design with a central 8 m mirror, are considered. Point spread function plots and encircled energy calculations show that there is no significant diffraction performance difference between the options except that hexagonal segments in the 1 m point-to-point range appear to deliver poorer PSFs as compared to 2 m and larger segments. Plans for implementation of a Matlab based integrated telescope model are discussed. A summary of adaptive optics system issues for large telescopes is presented along with plans for future research in AO.

A bibliometric analysis of observatory publications for the period 2008-2012

The primary scientific output from an astronomical telescope is the collection of papers published in refereed journals. A telescopes productivity is measured by the number of papers published which are based upon data taken with the telescope. The scientific impact of a paper can be measured quantitatively by the number of citations that the paper receives. In this paper I will examine the productivity and impact of over 20 telescopes, mainly optical/IR, with apertures larger than 3.5-m for the years between 2008 and 2012.

Gemini Observatory: Five years of multi-instrument queue operations

Gemini Observatory has operated Gemini North and South in multi-instrument queue mode since 2005. Each telescope has about 85% of the time scheduled for science, of which 90% are in queue mode. More than one instrument is used 75-80% of all science nights. We present on-sky performance data from the last five years: Completion rates for queue programs, open-shutter performance, and acquisition times. Open-shutter performance and acquisition times are competitive with other 8-10 meter-class telescopes for which data are available. We give an overview over how the queue is populated, planned and executed.

Canada's Dominion Astrophysical Observatory and the rise of 20th Century Astrophysics and Technology

Construction of Canada’s Dominion Astrophysical Observatory (DAO) commenced in 1914 with first light on 6 May 1918. As distinct from the contemporaneous development with private funding of major observatories in the western United States, DAO was (and remains) funded by the federal government. Canada’s initial foray into ‘big science’, creation of DAO during the First World War was driven by Canada’s desire to contribute significantly to the international rise of observational astrophysics enabled by photographic spectroscopy. In 2009 the Observatory was designated a National Historic Site. DAO’s varied, rich contributions to the astronomical heritage of the 20th century continue in the 21st century, with particularly strong ties to Maunakea.