571 research outputs found
Asymptotic Giant Branch Variables in the Galaxy and the Local Group
AGB variables, particularly the large amplitude Mira type, are a vital step
on the distance scale ladder. They will prove particularly important in the era
of space telescopes and extremely large ground-based telescopes with adaptive
optics, which will be optimized for infrared observing. Our current
understanding of the distances to these stars is reviewed with particular
emphasis on improvements that came from Hipparcos as well as on recent work on
Local Group galaxies. In addition to providing the essential calibration for
extragalactic distances Gaia may also provide unprecedented insight into the
poorly understood mass-loss process itself.Comment: Accepted for publication in Astrophysics and Space Science. From a
presentation at the conference "The Fundamental Cosmic Distance Scale: State
of the Art and Gaia Perspective, Naples May 2011. 8 Pages, 9 Figure
Cepheid Parallaxes and the Hubble Constant
Revised Hipparcos parallaxes for classical Cepheids are analysed together
with 10 HST-based parallaxes (Benedict et al.). In a reddening-free V,I
relation we find that the coefficient of logP is the same within the
uncertainties in our Galaxy as in the LMC, contrary to some previous
suggestions. Cepheids in the inner region of NGC4258 with near solar
metallicities (Macri et al.) confirm this result. We obtain a zero-point for
the reddening-free relation and apply it to Cepheids in galaxies used by
Sandage et al. to calibrate the absolute magnitudes of SNIa and to derive the
Hubble constant. We revise their result from 62 to 70+/-5 km/s/Mpc. The
Freedman et al. 2001 value is revised from 72 to 76+/-8 km/s/Mpc. These results
are insensitive to Cepheid metallicity corrections. The Cepheids in the inner
region of NGC4258 yield a modulus of 29.22+/-0.03(int) compared with a
maser-based modulus of 29.29+/-0.15. Distance moduli for the LMC, uncorrected
for any metallicity effects, are; 18.52+/-0.03 from a reddening-free relation
in V,I; 18.47+/-0.03 from a period-luminosity relation at K; 18.45+/-0.04 from
a period-luminosity-colour relation in J,K. Adopting a metallicity correction
in V,I from Marci et al. leads to a true LMC modulus of 18.39+/-0.05.Comment: 9 pages, 1 figure, on-line material from [email protected].
Accepted for MNRA
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
OpenEssayist: a supply and demand learning analytics tool for drafting academic essays
This paper focuses on the use of a natural language analytics engine to provide feedback to students when preparing an essay for summative assessment. OpenEssayist is a real-time learning analytics tool, which operates through the combination of a linguistic analysis engine that processes the text in the essay, and a web application that uses the output of the linguistic analysis engine to generate the feedback. We outline the system itself and present analysis of observed patterns of activity as a cohort of students engaged with the system for their module assignments. We report a significant positive correlation between the number of drafts submitted to the system and the grades awarded for the first assignment. We can also report that this cohort of students gained significantly higher overall grades than the students in the previous cohort, who had no access to OpenEssayist. As a system that is content free, OpenEssayist can be used to support students working in any domain that requires the writing of essays
The effect of dust obscuration in RR Tel on optical and IR long-term photometry and Fe II emission lines
Infrared and optical photometric and spectroscopic observations of the
symbiotic nova RR Tel are used to study the effects and properties of dust in
symbiotic binaries containing a cool Mira component, as well as showing
"obscuration events" of increased absorption, which are typical for such Miras.
A set of photometric observations of the symbiotic nova RR Tel in different
wavelength bands - visual from 1949 to 2002 and near-infrared (JHKL) from 1975
to 2002 - are presented. The variability due to the normal Mira pulsation was
removed from the JHKL data, which were then compared with the AAVSO visual
light curve. The changes of the Fe II emission line fluxes during the 1996-2000
obscuration episode were studied in the optical spectra taken with the
Anglo-Australian telescope.
We discuss the three periods during which the Mira component was heavily
obscured by dust as observed in the different wavelength bands. A change in the
correlations of J with other infrared magnitudes was observed with the colour
becoming redder after JD2446000. Generally, J-K was comparable, while K-L was
larger than typical values for single Miras. A distance estimate of 2.5 kpc,
based on the IR data, is given. A larger flux decrease for the permitted than
for the forbidden Fe II lines, during the obscuration episode studied, has been
found. There is no evidence for other correlations with line properties, in
particular with wavelength, which suggests obscuration due to separate
optically thick clouds in the outer layers.Comment: 19 pages, 11 figures, 3 table
Constraints on z~10 Galaxies from the Deepest HST NICMOS Fields
We use all available fields with deep NICMOS imaging to search for J dropouts
(H<28) at z~10. Our primary data set for this search were the two J+H NICMOS
parallel fields taken with the ACS HUDF. The 5 sigma limiting mags were 28.6 in
J and 28.5 in H. Several shallower fields were also used: J+H NICMOS frames
available over the HDF North, the HDF South NICMOS parallel, and the ACS HUDF.
The primary selection criterion was (J-H)>1.8. 11 such sources were found in
all search fields using this criterion. 8 of these were clearly ruled out as
credible z~10 sources, either as a result of detections (>2 sigma) blueward of
J or their colors redward of the break (H-K~1.5). The nature of the 3 remaining
sources could not be determined from the data. The number appears consistent
with the expected contamination from low-z interlopers. Analysis of the stacked
images for the 3 candidates also suggests contamination. Regardless of their
true redshifts, the actual number of z~10 sources must be <=3. To assess the
significance of these results, two lower redshift samples (a z~3.8 B-dropout
and z~6 i-dropout sample) were projected to z~8-12 using a (1+z)^{-1} size
scaling. They were added to the image frames, and the selection repeated,
giving 15.6 and 4.8 J-dropouts, respectively. This suggests that to the limit
of this probe (0.3 L*) there has been evolution from z~3.8 and possibly from
z~6. This is consistent with the strong evolution already noted at z~6 and
z~7.5 relative to z~3-4. Even assuming that 3 sources from this probe are at
z~10, the rest-frame continuum UV (~1500 A) luminosity density at z~10
(integrated down to 0.3 L*) is just 0.19_{-0.09}^{+0.13}x that at z~3.8 (or
0.19_{-0.10}^{+0.15}x including cosmic variance). However, if none of our
sources is at z~10, this ratio has a 1 sigma upper limit of 0.07. (abridged)Comment: 13 pages, 3 figures, 2 tables, accepted for publication in the
Astrophysical Journal Letter
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
El proyecto nefreduca : una plataforma educativa virtual para alumnos de secundaria hospitalizados por enfermedades crónicas de riñón
A pesar de avances médicos los jóvenes con enfermedades crónicas a menudo son hospitalizados durante largos períodos, y por consiguiente, no pueden mantener un ritmo de asistencia escolar normal. Esto puede traducirse a menudo en un menor nivel de alfabetización científica. A pesar de que muchos hospitales disponen de Aula hospitalaria; el acceso de estos jóvenes al currículum de ciencias es reducido, por falta de docentes especialistas y de los recursos específicos a estas y el contexto hospitalario. Con la finalidad de tratar estos problemas, se diseñó el proyecto Nefreduca. Esta comunicación presenta una tipología preliminar de las modificaciones de diseño basadas en evidencias a partir de los datos fase cíclica del proyecto. Los resultados muestran dos limitaciones principales a tener en cuenta en la enseñanza de las ciencias en el contexto educativo hospitalario
Lithium in the Symbiotic Mira V407 Cyg
We report an identification of the lithium resonance doublet LiI 6708A in the
spectrum of V407 Cyg, a symbiotic Mira with a pulsation period of about 745
days. The resolution of the spectra used was R~18500 and the measured
equivalent width of the line is ~0.34A. It is suggested that the lithium
enrichment is due to hot bottom burning in the intermediate mass AGB variable,
although other possible origins cannot be totally ruled out. In contrast to
lithium-rich AGB stars in the Magellanic clouds, ZrO 5551A, 6474A absorption
bands were not found in the spectrum of V407Cyg. These are the bands used to
classify the S-type stars at low-resolution. Although we identified weak ZrO
5718A, 6412A these are not visible in the low-resolution spectra, and we
therefore classify the Mira in V407 Cyg as an M type. This, together with other
published work, suggests lithium enrichment can precede the third dredge up of
s-process enriched material in galactic AGB stars.Comment: 4 pages, 2 figures, to be published in MNRA
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