100 research outputs found
Discovery of > 200 RR Lyrae Variables in M62: An Oosterhoff I Globular Cluster with a Predominantly Blue HB
We report on the discovery of a large number of RR Lyrae variable stars in
the moderately metal-rich Galactic globular cluster M62 (NGC 6266), which
places it among the top three most RR Lyrae-rich globular clusters known.
Likely members of the cluster in our studied field, from our preliminary number
counts, include about 130 fundamental-mode (RRab) pulsators, with =
0.548 d, and about 75 first-overtone (RRc) pulsators, with = 0.300 d.
The average periods and the position of the RRab variables with well-defined
light curves in the Bailey diagram both suggest that the cluster is of
Oosterhoff type I. However, the morphology of the cluster's horizontal branch
(HB) is strikingly similar to that of the Oosterhoff type II globular cluster
M15 (NGC 7078), with a dominant blue HB component and a very extended blue
tail. Since M15 and M62 differ in metallicity by about one dex, we conclude
that metallicity, at a fixed HB type, is a key parameter determining the
Oosterhoff status of a globular cluster and the position of its variables in
the Bailey diagram.Comment: 5 pages, 4 figures. ApJ Letters, in pres
The Absence of Extra-Tidal Structure in the Sculptor Dwarf Spheroidal Galaxy
The results of a wide-field survey of the Sculptor dwarf spheroidal galaxy
are presented. Our aims were to obtain an accurate map of the outer structure
of Sculptor, and to determine the level of interaction between this system and
the Galaxy. Photometry was obtained in two colours down to the magnitude limits
of V=20 and I=19, covering a 3.1 times 3.1 square deg area centred on Sculptor.
The resulting colour-magnitude data were used as a mask to select candidate
horizontal branch and red giant branch stars for this system. Previous work has
shown that the red horizontal branch (HB) stars are more concentrated than the
blue HB stars. We have determined the radial distributions of these two
populations and show that the overall Sculptor density profile is well
described by a two component model based on a combination of these radial
distributions. Additionally, spectra of the Ca ii triplet region were obtained
for over 700 candidate red giant stars over the 10 square deg region using the
2dF instrument on the Anglo-Australian Telescope. These spectra were used to
remove foreground Galactic stars based on radial velocity and Ca ii triplet
strength. The final list of Sculptor members contained 148 stars, seven of
which are located beyond the nominal tidal radius. Both the photometric and
spectroscopic datasets indicate no significant extra-tidal structure. These
results support at most a mild level of interaction between this system and the
Galaxy, and we have measured an upper mass limit for extra-tidal material to be
2.3 +/- 0.6% of the Sculptor luminous mass. This lack of tidal interaction
indicates that previous velocity dispersion measurements (and hence the amount
of dark matter detected) in this system are not strongly influenced by the
Galactic tidal field.Comment: 53 pages, 23 figures. Accepted for publication in the Astronomical
Journal. Some figures are reduced in size, and a full version is available
at: ftp://ftp.mso.anu.edu.au/pub/coleman/sculptor.pd
Exploring Halo Substructure with Giant Stars. VI. Extended Distributions of Giant Stars Around the Carina Dwarf Spheroidal Galaxy -- How Reliable Are They?
The question of the existence of active tidal disruption around various dSph
galaxies remains controversial. That debate often centers on the nature (bound
vs. unbound) of extended populations of stars. However, the more fundamental
issue of the very existence of the extended populations is still contentious.
We present an evaluation of the debate centering on one particular dSph,
Carina, for which claims both for and against the existence of stars beyond the
King radius have been made. Our review includes an examination of all previous
studies bearing on the Carina radial profile and shows that the survey method
which achieves the highest detected dSph signal-to-background in the outer
parts of the galaxy is the Washington M, T2 + DDO51 (MTD) filter approach from
Paper II in this series. We then address statistical methods used to evaluate
the reliability of MTD surveys in the presence of photometric errors and for
which a new, a posteriori statistical analysis methodology is provided.
Finally, these statistical methods are tested by new spectroscopy of stars in
the MTD-selected Carina candidate sample. Of 74 candidate giants with follow-up
spectroscopy, the MTD technique identified 61 new Carina members, including 8
stars outside the King radius. From a sample of 29 stars not initially
identified as candidate Carina giants but that lie just outside of our
selection criteria, 12 have radial velocities consistent with membership,
including 5 extratidal stars. Carina is shown to have an extended population of
giant stars extending to a major axis radius of 40' (1.44x the nominal King
radius).Comment: 56 pages, 10 figures. Submitted to the Astronomical Journal, 2004 Sep
2
Analysis of a Proper-Motion Selected Sample of Stars in the Ursa Minor Dwarf Spheroidal Galaxy
We have studied the stellar population and internal structure of the core of
the Ursa Minor dwarf spheroidal galaxy, using a sample of stars selected to be
members based on their proper motions. In agreement with previous studies, we
find Ursa Minor to be dominated by an old, metal-poor stellar population. A
small number of stars with high membership probabilities lie redward of the red
giant branch. The brightest (V <= 18) such stars are known to be Carbon stars,
rather than metal-rich first-ascent giants. A number of stars with high
membership probabilities lie blueward of the red giant branch, and are more
luminous than the horizontal branch. We speculate that these are
post-horizontal branch stars. There may also be one or two stars in the
post-AGB phase. Spectroscopy of the candidate post-HB and post-AGB stars is
required to determine their nature. We recover the internal substructure in
Ursa Minor that has been noted by several authors in the last 15 years. Using a
variety of two- and three-dimensional statistical tests, we conclude that this
substructure is statistically significant at the 0.005 level. There is no
evidence that the regions of density excess have stellar populations that
differ from the main body of Ursa Minor. The crossing time for a typical
density excess is only ~5 million years. They are therefore clearly not due to
intermediate age star-forming bursts. We conclude that they are instead due to
tidal interactions between the Galaxy and Ursa Minor.Comment: LaTeX with AASTeX style file, 22 pages with 7 figures. Accepted for
publication in The Astronomical Journal (Dec. 2001
The Globular Cluster Omega Centauri and the Oosterhoff Dichotomy
CCD observations obtained by the OGLE team for 128 RR Lyrae variables in
Omega Cen have been analysed. The P-L and P-A plots indicate that, in addition
to fundamental (RRab) and first overtone (RRc) pulsators, the Omega Cen RR
Lyrae population seems to include second overtone (RRe) and possibly third
overtone pulsators. The mean periods derived for the RRab and RRc stars are
typical values for an Oosterhoff type II (OoII) cluster. Nevertheless, the P-A
plot plot also shows that some of the RR Lyrae variables have `Oosterhoff type
I' (OoI) characteristics. Relative luminosities derived for the RRc variables
from Fourier coefficients correlate with the observed apparent magnitudes.
Masses for the RRc stars have been calculated from Fourier coefficients. A
comparison of the derived masses for RRc stars in the four OoII clusters Omega
Cen, M15, M55 and M68 indicates that the masses of the RRc stars in M15 and M68
are almost 0.2 solar masses greater than those in the other two. Since M15 and
M68 have a high frequency of RRd stars among their first overtone pulsators,
while none have been identified in Omega Cen or M55, this suggests that the
double-mode pulsation phenomenon may be associated with mass. Among the RRc
variables in Omega Cen, the OoII variables have lower derived masses and higher
luminosities than the OoI variables. An application of the period-density law
to pairs of OoI and OoII RRab stars selected according to their position in the
P-A plot also indicates that the OoII variables in general have lower masses
and higher luminosities. These findings support the hypothesis that RR Lyrae
variables in OoII systems are evolved HB stars that spend their ZAHB phase on
the blue side of the instability strip.Comment: 52 pages, 10 figures, to appear in the AJ (November 2000
Abundance Patterns in the Draco, Sextans and Ursa Minor Dwarf Spheroidal Galaxies
The Keck I telescope has been used to obtain HIRES spectra for red giants
belonging to the Draco, Sextans and Ursa Minor dwarf spheroidal (dSph)
galaxies. An analysis of these spectra is presented, along with abundance
ratios for more than 20 elements. The resulting database of element abundances
for 17 stars is the most extensive yet assembled for stars in dSph
environments. Our main findings are summarized as follows: (1) There is
unambiguous evidence for a large internal spread in metallicity in all three
galaxies: our program stars span a range of [Fe/H] = 1.53, 1.40 and 0.73 dex in
Draco, Sextans and Ursa Minor, respectively. (2) The abundance patterns among
the dSph stars are remarkably uniform, suggesting that all three galaxies have
similar nucleosynthetic histories. (3) A comparison of the measured abundance
ratios for our sample of dSph stars with published values for Galactic halo and
disk field stars suggests that the dSph galaxies have 0.02 < [alpha/Fe] < 0.13
dex, whereas the halo field star sample has [alpha/Fe] ~ 0.28 dex over the same
range in metallicity. (4) The most metal-rich dSph stars in our sample have
[Y/Fe] abundances which are significantly lower than those measured for halo
field stars of similar metallicity, while the measured [Ba/Eu] ratios for the
dSph stars suggest that the early chemical evolution of these galaxies was
dominated by the r-process. Taken together, these results suggest that the
Galactic halo is unlikely to have assembled, in its entirety, through the
disruption of dwarf galaxies similar to the low-luminosity dSphs studied here.
(ABRIDGED).Comment: 24 pages, 8 postscript figures (including 6 color figures). Accepted
for publication in the Astrophysical Journa
Effectiveness and cost-effectiveness of an internet intervention for family caregivers of people with dementia: design of a randomized controlled trial
<p>Abstract</p> <p>Background</p> <p>The number of people with dementia is rising rapidly as a consequence of the greying of the world population. There is an urgent need to develop cost effective approaches that meet the needs of people with dementia and their family caregivers. Depression, feelings of burden and caregiver stress are common and serious health problems in these family caregivers. Different kinds of interventions are developed to prevent or reduce the negative psychological consequences of caregiving. The use of internet interventions is still very limited, although they may be a cost effective way to support family caregivers in an earlier stage and diminish their psychological distress in the short and longer run.</p> <p>Methods/design</p> <p>A pragmatic randomized controlled trial is designed to evaluate the effectiveness and cost-effectiveness of ‘Mastery over Dementia’, an internet intervention for caregivers of people with dementia. The intervention aims at prevention and decrease of psychological distress, in particular depressive symptoms. The experimental condition consists of an internet course with 8 sessions and a booster session over a maximum period of 6 months guided by a psychologist. Caregivers in the comparison condition receive a minimal intervention. In addition to a pre and post measurement, an intermediate measurement will be conducted. In addition, there will be two follow-up measurements 3 and 6 months after post-treatment in the experimental group only. To study the effectiveness of the intervention, depressive symptoms are used as the primary outcome, whereas symptoms of anxiety, role overload and caregiver perceived stress are used as secondary outcomes. To study which caregivers profit most of the internet intervention, several variables that may modify the impact of the intervention are taken into account. Regarding the cost-effectiveness, an economic evaluation will be conducted from a societal perspective.</p> <p>Discussion</p> <p>This study will provide evidence about the effectiveness and cost-effectiveness of an internet intervention for caregivers. If both can be shown, this might set the stage for the development of a range of internet interventions in the field of caregiving for people with dementia. This is even more important because future generations of caregivers will be more familiar with the use of internet.</p> <p>Trial registration</p> <p>NTR-2051/RCT-DDB</p
Two cases of "cannabis acute psychosis" following the administration of oral cannabis
BACKGROUND: Cannabis is the most commonly used illegal drug and its therapeutic aspects have a growing interest. Short-term psychotic reactions have been described but not clearly with synthetic oral THC, especially in occasional users. CASE PRESENTATIONS: We report two cases of healthy subjects who were occasional but regular cannabis users without psychiatric history who developed transient psychotic symptoms (depersonalization, paranoid feelings and derealisation) following oral administration of cannabis. In contrast to most other case reports where circumstances and blood concentrations are unknown, the two cases reported here happened under experimental conditions with all subjects negative for cannabis, opiates, amphetamines, cocaine, benzodiazepines and alcohol, and therefore the ingested dose, the time-events of effects on behavior and performance as well as the cannabinoid blood levels were documented. CONCLUSION: While the oral route of administration achieves only limited blood concentrations, significant psychotic reactions may occur
Cognitive Behavioral Therapy versus Short Psychodynamic Supportive Psychotherapy in the outpatient treatment of depression: a randomized controlled trial
<p>Abstract</p> <p>Background</p> <p>Previous research has shown that Short Psychodynamic Supportive Psychotherapy (SPSP) is an effective alternative to pharmacotherapy and combined treatment (SPSP and pharmacotherapy) in the treatment of depressed outpatients. The question remains, however, how Short Psychodynamic Supportive Psychotherapy compares with other established psychotherapy methods. The present study compares Short Psychodynamic Supportive Psychotherapy to the evidence-based Cognitive Behavioral Therapy in terms of acceptability, feasibility, and efficacy in the outpatient treatment of depression. Moreover, this study aims to identify clinical predictors that can distinguish patients who may benefit from either of these treatments in particular. This article outlines the study protocol. The results of the study, which is being currently carried out, will be presented as soon as they are available.</p> <p>Methods/Design</p> <p>Adult outpatients with a main diagnosis of major depressive disorder or depressive disorder not otherwise specified according to DSM-IV criteria and mild to severe depressive symptoms (<it>Hamilton Depression Rating Scale </it>score ≥ 14) are randomly allocated to Short Psychodynamic Supportive Psychotherapy or Cognitive Behavioral Therapy. Both treatments are individual psychotherapies consisting of 16 sessions within 22 weeks. Assessments take place at baseline (week 0), during the treatment period (week 5 and 10) and at treatment termination (week 22). In addition, a follow-up assessment takes place one year after treatment start (week 52). Primary outcome measures are the number of patients refusing treatment (acceptability); the number of patients terminating treatment prematurely (feasibility); and the severity of depressive symptoms (efficacy) according to an independent rater, the clinician and the patient. Secondary outcome measures include general psychopathology, general psychotherapy outcome, pain, health-related quality of life, and cost-effectiveness. Clinical predictors of treatment outcome include demographic variables, psychiatric symptoms, cognitive and psychological patient characteristics and the quality of the therapeutic relationship.</p> <p>Discussion</p> <p>This study evaluates Short Psychodynamic Supportive Psychotherapy as a treatment for depressed outpatients by comparing it to the established evidence-based treatment Cognitive Behavioral Therapy. Specific strengths of this study include its strong external validity and the clinical relevance of its research aims. Limitations of the study are discussed.</p> <p>Trial registration</p> <p>Current Controlled Trails ISRCTN31263312</p
Effectiveness of behavioural graded activity compared with physiotherapy treatment in chronic neck pain: design of a randomised clinical trial [ISRCTN88733332]
BACKGROUND: Chronic neck pain is a common complaint in the Netherlands with a point prevalence of 14.3%. Patients with chronic neck pain are often referred to a physiotherapist and, although many treatments are available, it remains unclear which type of treatment is to be preferred. The objective of this article is to present the design of a randomised clinical trial, Ephysion, which examines the clinical and cost effectiveness of behavioural graded activity compared with a physiotherapy treatment for patients with chronic non-specific neck pain. METHODS: Eligible patients with non-specific neck pain persisting longer than 3 months will be randomly allocated to either the behavioural graded activity programme or to the physiotherapy treatment. The graded activity programme is based on an operant approach, which uses a time-contingent method to increase the patient's activity level. This treatment is compared with physiotherapy treatment using a pain-contingent method. Primary treatment outcome is the patient's global perceived effect concerning recovery from the complaint. Global perceived effect on daily functioning is also explored as primary outcome to establish the impact of treatment on daily activity. Direct and indirect costs will also be assessed. Secondary outcomes include the patient's main complaints, pain intensity, medical consumption, functional status, quality of life, and psychological variables. Recruitment of patients will take place up to the end of the year 2004 and follow-up measurement will continue until end 2005
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