3,148 research outputs found
The Stellar Populations of NGC 3109: Another Dwarf Irregular Galaxy with a Population II Stellar Halo
We have obtained V and I-band photometry for about 17500 stars in the field
of the dwarf irregular galaxy NGC3109, located in the outskirts of the Local
Group. The photometry allows us to study the stellar populations present inside
and outside the disk of this galaxy. From the VI color-magnitude diagram we
infer metallicities and ages for the stellar populations in the main body and
in the halo of NGC3109. The stars in the disk of this galaxy have a wide
variety of ages, including very young stars with approximately 10^7 yr. Our
main result is to establish the presence of a halo consisting of population II
stars, extending out to about 4.5 arcmin (or 1.8 kpc) above and below the plane
of this galaxy. For these old stars we derive an age of > 10 Gyr and a
metallicity of [Fe/H] = -1.8 +/- 0.2. We construct a deep luminosity function,
obtaining an accurate distance modulus (m-M)_0 = 25.62 +/- 0.1 for this galaxy
based on the I-magnitude of the red giant branch (RGB) tip and adopting E(V-I)
= 0.05.Comment: Accepted for publication in the Astronomical Journal 23 pages, latex,
12 Figures (Fig 1 not available in electronic format
A new HCN maser in IRAS 15082-4808
We have identified a new vibrational HCN maser at 89.087 GHz in the
asymptotic giant branch (AGB) star IRAS 15082-4808, a maser which is thought to
trace the innermost region of an AGB envelope. The observations of this maser
at three epochs are presented: two positive detections and one null detection.
The line profile has varied between the positive detections, as has the
intensity of the maser. The major component of the maser is found to be offset
by -2.0+/-0.9 km/s with respect to the systemic velocity of the envelope, as
derived from the 88.631 GHz transition of HCN. Similar blueshifts are measured
in the other 9 sources where this maser has been detected. Maser variability
with pulsation phase has been investigated for the first time using the 10
stars now available. Comparisons with AGB model atmospheres constrain the
position of the formation region of the maser to the region between the
pulsation shocks and the onset of dust acceleration, between 2 and 4 stellar
radii.Comment: 11 pages, 10 figures, accepted MNRAS, minor correction to equation
Short term consultant's final report.
The objective of the consultant's m~ss~on, as speeified in the job deseription attaehed to his appointment letter ref. ZS/BBEC-1422 dated June 1st, 1982, was: to advise the CPATSA to improve its researeh in drainage and salinity. After consultation with Dr Antonio Jose Simoes, aeting-head, and Dr Edson Lustoza de Possídio, technical director of CPATSA, eonsiderable time was devoted to review the reports and also a large amount of as yet unreported data of eoneluded investigations by CPATSA, as well as to get acquainted with the projeets and present stage of progress of the ongoing investigations. The investigations on salinity already coneluded by CPATSA were mostly dane in the são Gonçalo irrigation scheme in the state of Paraiba (Gilberto Gomes Cordeiro, research officer). Presently underway by CPATSA are a survey of the phreatie waterlevel fluetuation at the Bebedouro experiment station (Paulo Cesar Farias Gomes, research offieer) and an experiment on irrigation óf fodder grasses with rather saline well water of EC =2,6 mmhos/em in the dryland area at CPATSA (Jose Monteiro Soares, researeh offieer). Aetually most of the ongoing investigations are phreatic waterlevel and soil salinity surveys, whieh are carried out under the eoordination of CPATSA by the state enterprises .for agrieultural researeh in several DNOCS irrigation schemes, under an agreement between SUDENE/DNOCS/ EMBRAPA. For a better appreeiation of the problems, visits were made to these irrigation sehemes.bitstream/item/178994/1/FL-02984.pd
Mode switching in the nearby Mira-like variable R Doradus
We discuss visual observations spanning nearly 70 years of the nearby
semiregular variable R Doradus. Using wavelet analysis, we show that the star
switches back and forth between two pulsation modes having periods of 332 days
and about 175 days, the latter with much smaller amplitude. Comparison with
model calculations suggests that the two modes are the first and third radial
overtone, with the physical diameter of the star making fundamental mode
pulsation unlikely. The mode changes occur on a timescale of about 1000 d,
which is too rapid be related to a change in the overall thermal structure of
the star and may instead be related to weak chaos.
The Hipparcos distance to R Dor is 62.4 +/- 2.8 pc which, taken with its
dominant 332-day period, places it exactly on the period-luminosity relation of
Miras in the Large Magellanic Cloud. Our results imply first overtone pulsation
for all Miras which fall on the P-L relation. We argue that semiregular
variables with long periods may largely be a subset of Miras and should be
included in studies of Mira behaviour. The semiregulars may contain the
immediate evolutionary Mira progenitors, or stars may alternate between periods
of semiregular and Mira behaviour.Comment: 12 pages, latex with figures, accepted by MNRA
Millimeter polarisation of the protoplanetary nebula OH 231.8+4.2: A follow-up study with CARMA
In order to investigate the characteristics and influence of the magnetic
field in evolved stars, we performed a follow-up investigation of our previous
submillimeter analysis of the proto-planetary nebula (PPN) OH 231.8+4.2 (Sabin
et al. 2014), this time at 1.3mm with the CARMA facility in polarisation mode
for the purpose of a multi-scale analysis. OH 231.8+4.2 was observed at ~2.5"
resolution and we detected polarised emission above the 3-sigma threshold (with
a mean polarisation fraction of 3.5 %). The polarisation map indicates an
overall organised magnetic field within the nebula. The main finding in this
paper is the presence of a structure mostly compatible with an ordered toroidal
component that is aligned with the PPN's dark lane. We also present some
alternative magnetic field configuration to explain the structure observed.
These data complete our previous SMA submillimeter data for a better
investigation and understanding of the magnetic field structure in OH
231.8+4.2.Comment: 7 pages, 5 figures, 2 tables. Accepted for publication in MNRA
Third-dredge-up oxygen in planetary nebulae
The planetary nebulae He 2-436 and Wray 16-423 in the Sagittarius dwarf
galaxy appear to result from nearly twin stars, except that third-dredge-up
carbon is more abundant in He 2-436. A thorough photoionization-model analysis
implies that ratios Ne/O, S/O and Ar/O are significantly smaller in He 2-436,
indicative of third-dredge-up oxygen enrichment. The enrichment of oxygen with
respect to carbon is (7 +/- 4)%. Excess nitrogen in Wray 16-423 suggests third
dredge-up of late CN-cycle products even in these low-mass,
intermediate-metallicity stars.Comment: To appear in Astron. Astrophys. Lett. (Latex, 5 pages, 1 postscript
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