124 research outputs found
A Photometric Technique to Search for Be Stars in Open Clusters
We describe a technique to identify Be stars in open clusters using Stromgren
b, y, and narrow-band Halpha photometry. We first identify the B-type stars of
the cluster using a theoretical isochrone fit to the (b-y, y) color-magnitude
diagram. The strongest Be stars are easily identified in a (b-y, y-Halpha)
color-color diagram, but those with weaker Halpha emission (classified as
possible Be star detections) may be confused with evolved or foreground stars.
Here we present such photometry plus Halpha spectroscopy of members of the
cluster NGC 3766 to demonstrate the accuracy of our technique. Statistical
results on the relative numbers of Be and B-type stars in additional clusters
will be presented in a future paper.Comment: 15 pages, 6 figures, 1 table. Accepted by Ap
uvbyCa H beta CCD Photometry of Clusters. VII. The Intermediate-Age Anticenter Cluster Melotte 71
CCD photometry on the intermediate-band uvbyCa H beta system is presented for
the anticenter, intermediate-age open cluster, Melotte 71. Restricting the data
to probable single members of the cluster using the color-magnitude diagram and
the photometric indices alone generates a sample of 48 F dwarfs on the
unevolved main sequence. The average E(b-y) = 0.148 +/- 0.003 (s.e.m.) or
E(B-V) = 0.202 +/- 0.004 (s.e.m.), where the errors refer to internal errors
alone. With this reddening, [Fe/H] is derived from both m1 and hk, using H beta
and b-y as the temperature index, with excellent agreement among the four
approaches and a final weighted average of [Fe/H] = -0.17 +/- 0.02 (s.e.m.) for
the cluster, on a scale where the Hyades has [Fe/H] = +0.12. When adjusted for
the higher reddening estimate, the previous metallicity estimates from
Washington photometry and from spectroscopy are now in agreement with the
intermediate-band result. From comparisons to isochrones of appropriate
metallicity, the cluster age and distance are determined as 0.9 +/- 0.1 Gyr and
(m-M) = 12.2 +/- 0.1 or (m-M)_0 = 11.6 +/- 0.1. At this distance from the sun,
Mel 71 has a galactocentric distance of 10.0 kpc on a scale where the sun is
8.5 kpc from the galactic center. Based upon its age, distance, and elemental
abundances, Mel 71 appears to be a less populous analog to NGC 3960.Comment: Accepted for Astronomical Journal. 38 page latex file includes 11
figures and short version of data table. Full table will appear in online AJ
or may be requested from author
Understanding differing outcomes from semantic and phonological interventions with children with word-finding difficulties: a group and case series study
Developmental Language Disorder occurs in up to 10% of children and many of these children have difficulty retrieving words in their receptive vocabulary. Such word-finding difficulties (WFD) can impact social development and educational outcomes. This research aims to develop the evidence-base for supporting children with WFD and inform the design and analysis of intervention studies.
We included 20 children (age 6 to 8) with WFD each of whom participated in two interventions one targeting semantic attributes and the other phonological attributes of target words. The interventions, employing word-webs, were carefully constructed to facilitate direct comparison of outcome which was analysed at both group and case-series level.
The study used a robust crossover design with pre-intervention baseline, between–intervention wash-out and post-intervention follow-up testing. We incorporated: matching of item sets on individual performance at baseline, independent randomisation of order of intervention and items to condition, blinding of assessor, evaluation of fidelity and control items. The interventions were clinically feasible, with weekly sessions over six weeks.
Intervention improved children’s word-finding abilities with statistically significant change only during treatment phases of the study and not over baseline, wash-out or follow-up phases. For the group the semantic intervention resulted in a gain of almost twice as many items as the phonological intervention, a significant difference.
However, children differed in their response to intervention. Importantly, case-series analysis revealed outcomes predictable on the basis of children’s theoretically driven language profiles. Taking account of individual profiles in determining choice of intervention would enable more children to benefit.
The study provides new evidence to inform and refine clinical practice with this population. Future studies should be designed such that results can be analysed at both group and case series levels to extend theoretical understanding and optimise use of appropriate interventions
Galactic Structure Toward the Carina Tangent
This investigation presents a photometric study of the Galactic structure
toward the Carina arm tangent. The field is located between 280 deg and 286 deg
galactic longitude and -4 deg to 4 deg galactic latitude. All currently
available uvbybeta data is used to obtain homogeneous color excesses and
distances for more than 260 stars of spectral types O to G. We present revised
distances and average extinction for the open clusters and cluster candidates
NGC 3293, NGC 3114, Loden 46 and Loden 112. The cluster candidate Loden 112
appears to be a very compact group at a true distance modulus of 11.06 +\- 0.11
(s.e.) (1629 +84,-80 pc), significantly closer than previous estimates. We
found other OB stars at that same distance and, based on their proper motions,
suggest a new OB association at coordinates 282 deg < l < 285 deg, -2 deg < b <
2 deg. Utilizing BV photometry and spectral classification of the known O-type
stars in the very young open cluster Wd 2 we provide a new distance estimate of
14.13 +\-0.16 (s.e.) (6698 +512,-475 pc), in excellent agreement with recent
distance determinations to the giant molecular structures in this direction. We
also discuss a possible connection between the HII region RCW 45 and the
highly-reddened B+ star CPD -55 3036 and provide a revised distance for the
luminous blue variable HR Car.Comment: accepted to PAS
Catalog of Galactic Beta Cephei Stars
We present an extensive and up-to-date catalog of Galactic Beta Cephei stars.
This catalog is intended to give a comprehensive overview of observational
characteristics of all known Beta Cephei stars. 93 stars could be confirmed to
be Beta Cephei stars. For some stars we re-analyzed published data or conducted
our own analyses. 61 stars were rejected from the final Beta Cephei list, and
77 stars are suspected to be Beta Cephei stars. A list of critically selected
pulsation frequencies for confirmed Beta Cephei stars is also presented. We
analyze the Beta Cephei stars as a group, such as the distributions of their
spectral types, projected rotational velocities, radial velocities, pulsation
periods, and Galactic coordinates. We confirm that the majority of these stars
are multiperiodic pulsators. We show that, besides two exceptions, the Beta
Cephei stars with high pulsation amplitudes are slow rotators. We construct a
theoretical HR diagram that suggests that almost all 93 Beta Cephei stars are
MS objects. We discuss the observational boundaries of Beta Cephei pulsation
and their physical parameters. We corroborate that the excited pulsation modes
are near to the radial fundamental mode in frequency and we show that the mass
distribution of the stars peaks at 12 solar masses. We point out that the
theoretical instability strip of the Beta Cephei stars is filled neither at the
cool nor at the hot end and attempt to explain this observation
CCD uvbyHbeta Photometry in Clusters: I. The Open Cluster Standard, IC 4651
CCD photometry of the intermediate-age open cluster, IC 4651, on the
uvbyHbeta system is presented and analyzed. By using a combination of the
information from the color-magnitude diagram (CMD) and the color-color
diagrams, a sample of 98 highly probable main sequence cluster members with
high photometric accuracy is isolated. From this sample, adopting the intrinsic
color relation of Olsen (1988), E(b-y) = 0.062 +/- 0.003 and [Fe/H] = +0.077
+/- 0.012, where the errors quoted are the standard errors of the mean and
refer to the internal errors alone. Use of the Nissen (1988) intrinsic color
relation produces E(b-y) = 0.071 and [Fe/H] = +0.115. Adopting the lower
reddening, a direct main-sequence fit to the Hyades with (m-M) = 3.33 leads to
(m-M) = 10.15, while isochrones with convective overshoot and zeroed to the
Hyades produce an age of 1.7 +/- 0.1 Gyr, with an excellent match to the
morphology of the turnoff. The higher reddening produces (m-M) = 10.3 and an
age lower by 0.1 Gyr. Comparison with the CMD of NGC 3680 shows that the two
clusters have virtually identical morphology which, in combination with their
similar compositions, produces identical ages. Coincidentally, the shifts in
the CMD necessary to superpose the two clusters require that the apparent
moduli of IC 4651 and NGC 3680 be the same, while E(b-y)(4651) = E(b-y)(3680) +
0.04.Comment: 28 pages and 3 tables, in latex, 11 postscript figures. Accepted for
Astronomical Journa
A photometric mode identification method, including an improved non-adiabatic treatment of the atmosphere
We present an improved version of the method of photometric mode
identification of Heynderickx et al. (1994). Our new version is based on the
inclusion of precise non-adiabatic eigenfunctions determined in the outer
stellar atmosphere according to the formalism recently proposed by Dupret et
al.(2002). Our improved photometric mode identification technique is therefore
no longer dependent on ad hoc parameters for the non-adiabatic effects. It
contains the complete physical conditions of the outer atmosphere of the star,
provided that rotation does not play a key role. We apply our improved method
to the two slowly pulsating B stars HD 74560 and HD 138764 and to the beta
Cephei star EN (16) Lac. Besides identifying the degree l of the pulsating
stars, our method is also a tool for improving the knowledge of stellar
interiors and atmospheres, by imposing constraints on parameters such as the
metallicity and the mixing-length parameter alpha (a procedure we label
non-adiabatic asteroseismology).Comment: 10 pages, 9 figures Accepted for publication in Astronomy and
Astrophysic
A Search for Propylene Oxide and Glycine in Sagittarius B2 (LMH) and Orion
We have used the Mopra Telescope to search for glycine and the simple chiral
molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We
have not detected either species, but have been able to put sensitive upper
limits on the abundances of both molecules. The 3-sigma upper limits derived
for glycine conformer I are 3.7 x 10^{14} cm^{-2} in both Orion-KL and Sgr B2
(LMH), comparable to the reported detections of conformer I by Kuan et al.
However, as our values are 3-sigma upper limits rather than detections we
conclude that this weighs against confirming the detection of Kuan et al. We
find upper limits for the glycine II column density of 7.7 x 10^{12} cm^{-2} in
both Orion-KL and Sgr B2 (LMH), in agreement with the results of Combes et al.
The results presented here show that glycine conformer II is not present in the
extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA
results (Jones et al.) have ruled out the detection of glycine (both conformers
I and II) in the compact hot core of the LMH at the levels reported, so we
conclude that it is unlikely that Kuan et al. have detected glycine in either
Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of 3.0 x
10^{14} cm^{-2} in Orion-KL and 6.7 x 10^{14} cm^{-2} in Sgr B2 (LMH). We have
detected fourteen features in Sgr B2 and four features in Orion-KL which have
not previously been reported in the ISM, but have not be able to plausibly
assign these transitions to any carrier.Comment: 12 pages, 3 figures. Accepted by MNRAS 12th January 200
Spatially-resolved X-ray spectroscopy of the core of the Centaurus cluster
We present Chandra data from a 31.7 ks observation of the Centaurus cluster,
using the ACIS-S detector. Images of the X-ray emission show a plume-like
feature at the centre of the cluster, of extent 60 arcsec (20 kpc in
projection). The feature has the same metallicity as gas at a similar radius,
but is cooler. Using adaptive binning, we generate temperature, abundance and
absorption maps of the cluster core. The radial abundance profile shows that
the previously known, steep abundance gradient peaks with a metallicity of
1.3-1.8 Zsolar at a radius of about 45 arcsec (15 kpc), before falling back to
0.4 Zsolar at the centre of the cluster. A radial temperature profile shows
that the temperature decreases inwards. We determine the spatial distributions
of each of two temperature components, where applicable. The radiative cooling
time of the cooler component within the inner 10 arcsec (3 kpc) is less than
2x10^7 yr. X-ray holes in the image coincident with the radio lobes are seen,
as well as two outer sharp temperature drops, or cold fronts. The origin of the
plume is unclear. The existence of the strong abundance gradient is a strong
constraint on extensive convection or gas motion driven by a central radio
source.Comment: 11 pages, 14 figures (3 colour), accepted by MNRAS, high res. version
at http://www-xray.ast.cam.ac.uk/papers/cen1_accptd.pdf . Updated version
includes a section considering a non-thermal componen
- …