706 research outputs found
The Galactic Kinematics of Mira Variables
The galactic kinematics of Mira variables derived from radial velocities,
Hipparcos proper motions and an infrared period-luminosity relation are
reviewed. Local Miras in the 145-200day period range show a large asymmetric
drift and a high net outward motion in the Galaxy. Interpretations of this
phenomenon are considered and (following Feast and Whitelock 2000) it is
suggested that they are outlying members of the bulge-bar population and
indicate that this bar extends beyond the solar circle.Comment: 7 pages, 2 figure, to be published in Mass-Losing Pulsating Stars and
their Circumstellar Matter, Y. Nakada & M. Honma (eds) Kluwer ASSL serie
Luminosities of AGB Variables
The prevailing evidence suggests that most large-amplitude AGB variables
follow the period luminosity (PL) relation that has been established for Miras
in the LMC and galactic globular clusters. Hipparcos observations indicate that
most Miras in the solar neighbourhood are consistent with such a relation.
There are two groups of stars with luminosities that are apparently greater
than the PL relation would predict: (1) in the LMC and SMC there are large
amplitude variables, with long periods, P> 420 days, which are probably
undergoing hot bottom burning, but which are very clearly more luminous than
the PL relation (these are visually bright and are likely to be among the first
stars discovered in more distant intermediate age populations); (2) in the
solar neighbourhood there are short period, P<235 days, red stars which are
probably more luminous than the PL relation. Similar short-period red stars,
with high luminosities, have not been identified in the Magellanic Clouds.Comment: 8 pages, 2 figure, to be published in Mass-Losing Pulsating Stars and
their Circumstellar Matter, Y. Nakada & M. Honma (eds) Kluwer ASSL serie
Hipparcos period-luminosity relations for Miras and semiregular variables
We present period-luminosity diagrams for nearby Miras and semiregulars,
selecting stars with parallaxes better than 20 per cent and well-determined
periods. Using K-band magnitudes, we find two well-defined P-L sequences, one
corresponding to the standard Mira P-L relation and the second shifted to
shorter periods by a factor of about 1.9. The second sequence only contains
semiregular variables, while the Mira sequence contains both Miras and
semiregulars. Several semiregular stars show double periods in agreement with
both relations. The Whitelock evolutionary track is shown to fit the data,
indicating that the semiregulars are Mira progenitors. The transition between
the two sequences may correspond to a change in pulsation mode or to a change
in the stellar structure. Large amplitude pulsations leading to classical Mira
classification occur mainly near the tip of the local AGB luminosity function.Comment: 10 pages with figures, accepted by ApJ Letter
Imaging the Radio Photospheres of Mira Variables
We have used the VLA at 43 GHz to image the radio continuum emission from o
Ceti, R Leo, and W Hya and to precisely locate their SiO maser emission with
respect to the star. The radio continuum emission region for all three stars
has a diameter close to 5.6 AU. These diameters are similar to those measured
at infrared wavelengths in bands containing strong molecular opacity and about
twice those measured in line-free regions of the infrared spectrum. Thus, the
radio photosphere and the infrared molecular layer appear to be coextensive.
The 43 GHz continuum emission is consistent with temperatures near 1600 K and
opacity from H-minus free-free interactions. While the continuum image of o
Ceti appears nearly circular, both R Leo and W Hya display significant
elongations. The SiO masers for all three stars show partial rings with
diameters close to 8 AU.Comment: 14 pages; 3 figure
The Distance to the M31 Globular Cluster System
The distance to the centroid of the M31 globular cluster system is determined
by fitting theoretical isochrones to the observed red-giant branches of
fourteen globular clusters in M31. The mean true distance modulus of the M31
globular clusters is found to be 24.47 +/- 0.07 mag. This is consistent with
distance modulii for M31 that have been obtained using other distance
indicators.Comment: 11 pages, 2 postscript figures, uses aaspp4.sty, to be published in
the May 1998 Astronomical Journa
A New Kinematic Distance Estimator to the LMC
The distance to the Large Magellanic Cloud (LMC) can be directly determined
by measuring three of its properties, its radial-velocity field, its mean
proper motion, and the position angle \phi_ph of its photometric line of nodes.
Statistical errors of 2% are feasible based on proper motions obtained with any
of several proposed astrometry satellites, the first possibility being the
Full-Sky Astrometric Mapping Explorer (FAME). The largest source of systematic
error is likely to be in the determination of \phi_ph. I suggest two
independent methods to measure \phi_ph, one based on counts of clump giants and
the other on photometry of clump giants. I briefly discuss a variety of methods
to test for other sources of systematic errors.Comment: submitted to ApJ, 13 page
The Distances of SNR W41 and overlapping HII regions
New HI images from the VLA Galactic Plane Survey show prominent absorption
features associated with the supernovae remnant G23.3-0.3 (SNR W41). We
highlight the HI absorption spectra and the CO emission spectra of eight
small regions on the face of W41, including four HII regions, three non-thermal
emission regions and one unclassified region. The maximum velocity of
absorption for W41 is 782 km/s and the CO cloud at radial velocity
955 km/s is behind W41. Because an extended TeV source, a diffuse X-ray
enhancement and a large molecular cloud at radial velocity 775 km/s are
also projected at the center of W41, these yield the kinematic distance of 3.9
to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21
and G23.07+0.25 are at the far kinematic distances (9.9 kpc and
10.6 kpc respectively) of their recombination-line velocities (1030.5 km/s
and 89.62.1 km/s respectively), G23.07-0.37 is at the near kinematic
distance (4.40.3 kpc) of its recombination-line velocity (82.72.0
km/s), and G23.27-0.27 is probably at the near kinematic distance (4.10.3
kpc) of its recombination-line velocity (76.10.6 km/s).Comment: 11 pages, 3 figs., 2 tables, accepted by A
Long Period Variables in Globular Clusters and the Galactic Bulge: Their Dependence on Metallicity
We derive the frequency of occurrence of luminous long period variables
(LLPVs) in globular clusters and in the Baade's Window field of the Galactic
bulge. LLPVs occur only in clusters with [Fe/H]>/= -1.0. In these clusters
their frequency of occurrence relative to the number of giant stars appears to
be independent of metallicity. Integrated over all metallicities, Baade's
Window appears to be deficient in LLPVs. We estimate [Fe/H] values for Baade's
Window LLPVs from their period and a log P vs. [Fe/H] relation derived from
cluster variables and find that LLPVs with [Fe/H]>/= 0.0 are absent from
Baade's Window. We propose that this is because of enhanced mass loss rates in
these LLPVs with a consequently abbreviated lifetime compared to lower
metallicity LLPVs. A typical lifetime for cluster LLPVs is about 3 x10^5 yrs.
Finally, we call attention to the need for a much more complete survey for
LLPVs in globular clusters.Comment: 20 pages of text plus tables in PS format created by MS WORD97; 9
figures in PS format generated by SigmaPlot; all in one gzipped tar file;
originally submitted to ApJ but has now been accepted and is in press at the
AJ with minor revisions and some amplifications from previous versio
Passion and motivation for studying: Predicting academic engagement and burnout in university students
Research on the dualistic model of passion has investigated harmonious and obsessive passion in many domains. However, few studies have investigated passion for studying and the role passion for studying plays in student engagement and well-being. The present study investigated the relationships between harmonious and obsessive passion for studying and academic engagement (vigour, dedication and absorption) and burnout (exhaustion, cynicism and inefficacy) in 105 university students, controlling for the effects of autonomous and controlled motivation. Both harmonious and obsessive passion explained variance in academic engagement and burnout beyond autonomous and controlled motivation: harmonious passion predicted higher dedication and lower cynicism, obsessive passion predicted higher absorption, and both harmonious and obsessive passion predicted higher vigour and lower inefficacy. The findings suggest that passion for studying explains individual differences in students' academic engagement and burnout beyond autonomous and controlled motivation and thus deserves more attention from educational psychology. © 2011 Taylor & Francis
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