17 research outputs found
Photometry Results for the Globular Clusters M10 and M12: Extinction Maps, Color-Magnitude Diagrams, and Variable Star Candidates
We report on photometry results of the equatorial globular clusters (GCs) M10
and M12. These two clusters are part of our sample of GCs which we are probing
for the existence of photometrically varying eclipsing binary stars. During the
search for binaries in M10 and M12, we discovered the signature of differential
reddening across the fields of the clusters. The effect is stronger for M10
than for M12. Using our previously described dereddening technique, we create
differential extinction maps for the clusters which dramatically improve the
appearance of the color-magnitude diagrams (CMDs). Comparison of our maps with
the dust emissivity maps of Schlegel, Finkbeiner, & Davis (SFD) shows good
agreement in terms of spatial extinction features. Several methods of adding an
E_{V-I} zero point to our differential maps are presented of which isochrone
fitting proved to be the most successful. Our E_{V-I} values fall within the
range of widely varying literature values. More specifically, our reddening
zero point estimate for M12 agrees well with the SFD estimate, whereas the one
for M10 falls below the SFD value. Our search for variable stars in the
clusters produced a total of five variables: three in M10 and two in M12. The
M10 variables include a binary system of the W Ursa Majoris (W UMa) type, a
background RR Lyrae star, and an SX Phoenicis pulsator, none of which is
physically associated with M10. M12's variables are two W UMa binaries, one of
which is most likely a member of the cluster. We present the phased photometry
lightcurves for the variable stars, estimate their distances, and show their
locations in the fields and the CMDs of the GCs.Comment: 22 pages, 21 figures, to be published in AJ October 2002. For a
higher-resolution version of this paper, please visit
http://www.astro.lsa.umich.edu/~kaspar/M10_M12_photometry.ps.gz (gzipped
postscript) or http://www.astro.lsa.umich.edu/~kaspar/M10_M12_photometry.pdf
(pdf file
The Star Formation History of the Carina Dwarf Galaxy
We have analyzed deep B and V photometry of the Carina dwarf spheroidal
reaching below the old main-sequence turnoff to about V = 25. Using simulated
color-magnitude diagrams to model a range of star formation scenarios, we have
extracted a detailed, global star formation history. Carina experienced three
significant episodes of star formation at about 15 Gyr, 7 Gyr, and 3 Gyr.
Contrary to the generic picture of galaxy evolution, however, the bulk of star
formation, at least 50%, occured during the episode 7 Gyr ago, which may have
lasted as long as 2 Gyr. For unknown reasons, Carina formed only 10-20% of its
stars at an ancient epoch and then remained quiescent for more than 4 Gyr. The
remainder (~30%) formed relatively recently, only 3 Gyr ago. Interest in the
local population of dwarf galaxies has increased lately due to their potential
importance in the understanding of faint galaxy counts. We surmise that objects
like Carina, which exhibits the most extreme episodic behavior of any of the
dwarf spheroidal companions to the Galaxy, are capable of contributing to the
observed excess of blue galaxies at B = 24 only if the star formation occurred
instantaneously.Comment: 23 pages of text, 20 figures, 8 tables. AJ, in pres
Dwarf Cepheids in the Carina Dwarf Spheroidal Galaxy
We have discovered 20 dwarf Cepheids (DC) in the Carina dSph galaxy from the
analysis of individual CCD images obtained for a deep photometric study of the
system. These short-period pulsating variable stars are by far the most distant
(~100 kpc) and faintest (V ~ 23.0) DCs known. The Carina DCs obey a
well-defined period-luminosity relation, allowing us to readily distinguish
between overtone and fundamental pulsators in nearly every case. Unlike RR Lyr
stars, the pulsation mode turns out to be uncorrelated with light-curve shape,
nor do the overtone pulsators tend towards shorter periods compared to the
fundamental pulsators. Using the period-luminosity (PL) relations from Nemec et
al. (1994 AJ, 108, 222) and McNamara (1995, AJ, 109, 1751), we derive (m-M)_0 =
20.06 +/- 0.12, for E(B-V) = 0.025 and [Fe/H] = -2.0, in good agreement with
recent, independent estimates of the distance/reddening of Carina. The error
reflects the uncertainties in the DC distance scale, and in the metallicity and
reddening of Carina. The frequency of DCs among upper main sequence stars in
Carina is approximately 3%. The ratio of dwarf Cepheids to RR Lyr stars in
Carina is 0.13 +/- 0.10, though this result is highly sensitive to the
star-formation history of Carina and the evolution of the Horizontal Branch. We
discuss how DCs may be useful to search effectively for substructure in the
Galactic halo out to Galactocentric distances of ~100 kpc.Comment: 20 pages of text, 7 figure
Andromeda VIII - a New Tidally Distorted Satellite of M31
We report the detection of a new satellite of M31, projected close to M32.
And VIII is tidally distorted, with length ~10 kpc and width a few kpc. It
contains 5-12 planetary nebulae (PNe) and 1-3 globular clusters, and has a
velocity of -204 km/s with respect to M31, some 350 km/s away from M32's
velocity. There are also about 4 x 10^5 solar masses of HI, well-separated from
the disk, at the same position and velocity. The satellite has luminosity of
1.2-2.4 x 10^8 solar luminosities, and a central surface brightness of order
\mu_V=24. Both these values are typical of Local Group dwarf galaxies. Its
surface brightness is some 6 magnitudes brighter than any of the stellar
streams found in the Milky Way or M31. The three associated globular clusters
have reddening consistent with foreground reddening from the Milky Way only,
making it likely that the satellite is in front of M31, unlike the giant tidal
stream of Ibata et al.(2001), which is behind M31 in the SE quadrant. However,
the major axis of And VIII is aligned with the western edge of this giant
stream, and we suggest that its unusual fan shape is caused by superposition of
two streams, the westernmost of which was tidally stripped from And VIII.Comment: 11 pages, 2 figures. ApJ Letters, in pres
Population Gradients in Local Group Dwarf Spheroidals
We present a systematic and homogeneous analysis of population gradients for
the Local Group dwarf spheroidals (dSphs) Carina, Sculptor, Sextans, Tucana,
Andromeda I-III, V, and VI. For all of the Milky Way companions studied here we
find significant population gradients. The same is true for the remote dSph
Tucana located at the outskirts of the LG. Among the M 31 dSph companions only
Andromeda I and VI show obvious gradients. In all cases where a HB morphology
gradient is visible, the red HB stars are more centrally concentrated. The
occurence of a HB morphological gradient shows a correlation with a morphology
gradient in the red giant branch. It seems likely that metallicity is the
driver of the gradients in Sextans, Sculptor, Tucana, and Andromeda VI, while
age is an important factor in Carina. We find no evidence that the vicinity of
a nearby massive spiral galaxy influences the formation of the population
gradients.Comment: accepted for publication in AJ; 25 pages; 11 images in jpeg and png
forma
Planetary Nebulae Kinematics in M31
We present kinematics of 135 planetary nebulae in M31 from a survey covering
3.9 square degrees and extending out to 15 kpc from the southwest major axis
and more than 20 kpc along the minor axis. The majority of our sample, even
well outside the disk, shows significant rotational support (mean line-of-sight
velocity 116 km/s). We argue that these PN belong to the outer part of M31's
large de Vaucouleurs bulge. Only five PN have velocities clearly inconsistent
with this fast rotating bulge. All five may belong to tidal streams in M31's
outer halo. One is projected on the Northern Spur, and is counter-rotating with
respect to the disk there. Two are projected along the major axis at X=-10 kpc
and have M32-like velocities; they could be debris from that galaxy. The
remaining two halo PN are located near the center of the galaxy and their
velocities follow the gradient found by Ibata et al. (2004), implying that
these PN could belong to the Southern Stream. If M31 has a non-rotating,
pressure-supported halo, we have yet to find it, and it must be a very minor
component of the galaxy.Comment: accepted to ApJ; main body of paper is 36 pages, including 14 figure
BHPR research: qualitative1.âComplex reasoning determines patients' perception of outcome following foot surgery in rheumatoid arhtritis
Background: Foot surgery is common in patients with RA but research into surgical outcomes is limited and conceptually flawed as current outcome measures lack face validity: to date no one has asked patients what is important to them. This study aimed to determine which factors are important to patients when evaluating the success of foot surgery in RA Methods: Semi structured interviews of RA patients who had undergone foot surgery were conducted and transcribed verbatim. Thematic analysis of interviews was conducted to explore issues that were important to patients. Results: 11 RA patients (9 â, mean age 59, dis dur = 22yrs, mean of 3 yrs post op) with mixed experiences of foot surgery were interviewed. Patients interpreted outcome in respect to a multitude of factors, frequently positive change in one aspect contrasted with negative opinions about another. Overall, four major themes emerged. Function: Functional ability & participation in valued activities were very important to patients. Walking ability was a key concern but patients interpreted levels of activity in light of other aspects of their disease, reflecting on change in functional ability more than overall level. Positive feelings of improved mobility were often moderated by negative self perception ("I mean, I still walk like a waddling duckâ). Appearance: Appearance was important to almost all patients but perhaps the most complex theme of all. Physical appearance, foot shape, and footwear were closely interlinked, yet patients saw these as distinct separate concepts. Patients need to legitimize these feelings was clear and they frequently entered into a defensive repertoire ("it's not cosmetic surgery; it's something that's more important than that, you know?â). Clinician opinion: Surgeons' post operative evaluation of the procedure was very influential. The impact of this appraisal continued to affect patients' lasting impression irrespective of how the outcome compared to their initial goals ("when he'd done it ... he said that hasn't worked as good as he'd wanted to ... but the pain has goneâ). Pain: Whilst pain was important to almost all patients, it appeared to be less important than the other themes. Pain was predominately raised when it influenced other themes, such as function; many still felt the need to legitimize their foot pain in order for health professionals to take it seriously ("in the end I went to my GP because it had happened a few times and I went to an orthopaedic surgeon who was quite dismissive of it, it was like what are you complaining aboutâ). Conclusions: Patients interpret the outcome of foot surgery using a multitude of interrelated factors, particularly functional ability, appearance and surgeons' appraisal of the procedure. While pain was often noted, this appeared less important than other factors in the overall outcome of the surgery. Future research into foot surgery should incorporate the complexity of how patients determine their outcome Disclosure statement: All authors have declared no conflicts of interes
The star formation histories of the Carina and sculptor dwarf spheroidal galaxies.
Using simulated color-magnitude diagrams to model a range of star formation scenarios, we have extracted a detailed, global star formation history for two of the Galaxy's dwarf spheroidals. Carina experienced three significant episodes of star formation at ∼15 Gyr, 7 Gyr, and 3 Gyr. Contrary to the generic picture of galaxy evolution, however, the bulk of star formation, at least 50%, occurred during the episode 7 Gyr ago, which may have lasted as long as 2 Gyr. For unknown reasons, Carina formed only 10--20% of its stars at an ancient epoch and then remained quiescent for more than 4 Gyr. The remainder (∼30%) formed relatively recently, only 3 Gyr ago. Interest in the local population of dwarf galaxies has increased lately due to their potential importance in the understanding of faint galaxy counts. We surmise that objects like Carina, which exhibits the most extreme episodic behavior of any of the dwarf spheroidal companions to the Galaxy, are capable of contributing to the observed excess of blue galaxies at B ∼ 24 only if the star formation occurred over a very short timescale (∼10 Myr). We have applied the same methods to the CMD of the Sculptor dSph and infer that the dominant old population is ∼16 Gyr old and formed over a period of 2--3 Gyr, that as many as 30--60% of all apparently single stars in the inner region of Sculptor may be binaries, and that star formation continued at a low level characterized by bursts until ∼2 Gyr ago. Since we find no radial gradients in the age or metallicity distribution within Sculptor, neither age nor metallicity can individually account for the internal 'second parameter' problem observed within the galaxy. We speculate that the possible radial gradient in the binary-star population may be related to the variation of the HB morphology in Sculptor.Ph.D.AstronomyPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132382/2/9963812.pd