489 research outputs found
Red Supergiants in the Disk of M81: Tracing the Spatial Distribution of Star Formation 25 Million Years in the Past
Near-infrared images are used to investigate the brightest red stars in the
disk of the nearby spiral galaxy M81. Red supergiants (RSGs) form a
well-defined sequence on the color-magnitude diagrams (CMDs) that peaks near
M_K = -11.5; RSGs with this peak brightness are seen throughout all fields that
were studied, indicating that star formation occured over a large part of the
M81 disk only ~ 10 Myr in the past. The number of RSGs per unit integrated
K-band light is compared at various locations in the disk. We conclude that
star-forming activity in M81 during the past 10 - 25 Myr (1) was distributed
over a larger fraction of the disk than it is at the present day, and (2) was
not restricted to a given radial interval, but was distributed in a manner that
closely followed the stellar mass profile. Star counts indicate that the mean
SFR of M81 between 10 and 25 Myr in the past was ~ 0.1 solar masses per year,
which is not greatly different from the present day SFR estimated from Halpha
and FUV emission.Comment: 21 pages of text and 7 postscript figures; to appear in the PAS
Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies. II. NGC 247 and NGC 2403
J, H, and K' images obtained with the Canada-France-Hawaii Telescope adaptive
optics system are used to investigate the star-forming histories of the central
regions of the Sc galaxies NGC 247 and NGC 2403. The brightest resolved red
stars within 15 arcsec of the nucleus of each galaxy are red supergiants,
indicating that the central few hundred parsecs of these galaxies experienced
star formation within the last ~ 0.1 Gyr. However, when averaged over Gyr time
scales, the star-forming histories of the inner disks of these galaxies have
been remarkably similar, as expected if the long-term evolution of disks is
defined by local characteristics such as mass density. It is demonstrated that
NGC 247 and NGC 2403, like M33, harbour nuclear star clusters with stellar
contents that differ from the surrounding central light concentrations. The
nucleus of NGC 2403 is significantly bluer than that of the other two galaxies
and the K-band surface brightnesses near the centers of NGC 247 and NGC 2403
are 1 -- 2 mag per square arcsec lower than in M33. Finally, it is noted that
young or intermediate-age nuclear star clusters are a common occurence in
nearby spirals, indicating that nuclear star formation in these objects is
either continuous or episodic on time scales of 0.1 - 1 Gyr.Comment: 27 pages of text and 14 figures; to appear in the Astronomical
Journa
The Disk and Extraplanar Environment of NGC 247
The stellar content of the spiral galaxy NGC 247 is investigated. The main
sequence turn-off (MSTO) in the inner 12 kpc of the disk corresponds to an age
of 6 Myr. A mean star formation rate (SFR) of 0.1 solar masses per year during
the past 16 Myr is computed from star counts. The color of the red supergiant
plume does not change with radius, suggesting that the mean metallicity of
young stars does not vary by more than 0.1 dex. The number of bright main
sequence stars per local stellar mass density climbs towards larger radii out
to a distance of 12 kpc; the scale lengths that characterize the radial
distributions of young and old stars in the disk thus differ. The density of
bright main sequence stars with respect to projected HI mass gradually drops
with increasing radius. The population of very young stars disappears in the
outer disk; the MSTO at galactocentric radii between 12 and 15 kpc corresponds
to 16 Myr, while between 15 and 18 kpc the age is > 40 Myr. Red giant branch
(RGB) stars are resolved at a projected minor axis galactocentric distance of
12 kpc. There is a broad spread in metallicity among the RGB stars, with a mean
[M/H] = -1.2. The RGB-tip occurs at i' = 24.5 +/- 0.1, indicating that the
distance modulus is 27.9 +/- 0.1. Luminous AGB stars with an age 3 Gyr are also
seen in this field.Comment: Includes 16 eps figures; to appear in the Astrophysical Journa
Planetary Nebulae as standard candles XI. Application to Spiral Galaxies
We report the results of an [O III] lambda 5007 survey for planetary nebulae
(PN) in three spiral galaxies: M101 (NGC 5457), M51 (NGC 5194/5195) and M96
(NGC 3368). By comparing on-band/off-band [O III] lambda 5007 images with
images taken in H-alpha and broadband R, we identify 65, 64 and 74 PN
candidates in each galaxy, respectively. From these data, an adopted M31
distance of 770 kpc, and the empirical planetary nebula luminosity function
(PNLF), we derive distances to M101, M51, and M96 of 7.7 +/- 0.5, 8.4 +/- 0.6,
and 9.6 +/- 0.6 Mpc. These observations demonstrate that the PNLF technique can
be successfully applied to late-type galaxies, and provide an important overlap
between the Population I and Population II distance scales. We also discuss
some special problems associated with using the PNLF in spiral galaxies,
including the effects of dust and the possible presence of [O III] bright
supernova remnants.Comment: 38 pages, TeX, with tables included but not figures. Uses epsf.tex
and kpnobasic.tex. To be published in the Astophysical Journal. Full paper is
available at http://www.astro.psu.edu/users/johnf/Text/research.htm
The evolution of Palaeolake Flixton and the environmental context of Star Carr:An oxygen and carbon isotopic record of environmental change for the early Holocene
Use of environmental isotopes to assess the sustainability of intensively exploited aquifer systems (2012â2015)
Intensive exploitation of groundwater over longer period has led, in many important aquifers, to marked lowering of water tables, increasing exploitation costs, and often, to a progressive deterioration of water quality. Concentrated pumping may also alter flow patterns permanently with the risk of migration of pollutants into aquifers from the surrounding aquifers or surface water bodies due to lack of physical protection to prevent them. Isotope hydrology tools have proven to be very useful in assessing groundwater hydrology, addressing aspects related to recharge processes, delineation of flow patterns, water quality issues and interactions with other water bodies; this unique information can be further used to evaluate long term aquifer sustainability. The objective of the Coordinated Research Project F33019 is to develop and review approaches and methodologies, mostly based on the combined use of conventional hydrogeological techniques and environmental isotopes, to assess the response of groundwater systems to intensive exploitation and groundwater availability. Access to new dating tools and approaches for groundwater dating covering different time scales offers the possibility to evaluate changes in groundwater dynamics and flow patterns, providing key data to predict the evolution of aquifers and their sustainability as major sources of water. The CRP aims to assess the performance of these new tools and approaches and the possible adoption of these methods by water management experts
Effect of religiosity/spirituality and sense of coherence on depression within a rural population in Greece: the Spili III project
Background: Recent research has addressed the hypothesis that religiosity/spirituality and sense of coherence buffer the negative effects of stress on numerous health issues. The aim of the current study was to further this work by exploring potential links between psycho-social factors such as religiosity/ spirituality and sense of coherence with depression.
Methods: A total of 220 subjects of the SPILI III cohort (1988-2012) attending a primary care setting in the town of Spili on rural Crete represented the target group. All participants underwent a standardized procedure. Validated questionnaires were used to evaluate sense of coherence, depression levels and religious and spiritual beliefs. A multiple linear regression analysis of the Beck Depression Inventory Scale (BDI) in relation to demographic characteristics, scores on the Royal Free Interview for Spiritual and Religious Beliefs scale (RFI-SRB) and Sense of Coherence scale (SOC) was used.
Results: A significant inverse association was found between BDI and RFI-SRB scale (B-coef=-0.6999, p<0.001), as well as among BDI and SOC scale (B-coef=-0.556, p<0.001).
Conclusions: The findings of the current observational study indicate that highly religious participants are less likely to score high in the depression scale. Furthermore, participants with high SOC scored significantly low in the BDI scale. Further research is required in order to explore the potential effect of SOC and religiosity/spirituality in mental health
Loneliness, social support and cardiovascular reactivity to laboratory stress
Self-reported or explicit loneliness and social support have been inconsistently associated with cardiovascular reactivity (CVR) to stress. The present study aimed to adapt an implicit measure of loneliness, and use it alongside the measures of explicit loneliness and social support, to investigate their correlations with CVR to laboratory stress. Twenty-five female volunteers aged between 18 and 39 years completed self-reported measures of loneliness and social support, and an Implicit Association Test (IAT) of loneliness. The systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) reactivity indices were measured in response to psychosocial stress induced in the laboratory. Functional support indices of social support were significantly correlated with CVR reactivity to stress. Interestingly, implicit, but not explicit, loneliness was significantly correlated with DBP reactivity after one of the stressors. No associations were found between structural support and CVR indices. Results are discussed in terms of validity of implicit versus explicit measures and possible factors that affect physiological outcomes
Psychosocial factors are preventive against coronary events in Japanese men with coronary artery disease: The Eastern Collaborative Group Study 7.7-year follow-up experience
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