135 research outputs found
Discovery of Five New R Coronae Borealis Stars in the MACHO Galactic Bulge Database
We have identified five new R Coronae Borealis (RCB) stars in the Galactic
bulge using the MACHO Project photometry database, raising the total number of
known Galactic RCB stars to about 40. We have obtained spectra to confirm the
identifications. The fact that four out of the five newly identified RCB stars
are ``cool'' (T(eff) 6000 K) suggests
that the preponderance of warm RCB stars among the existing sample is a
selection bias. These cool RCB stars are redder and fainter than their warm
counterparts and may have been missed in surveys done with blue plates. Based
on the number of new RCB stars discovered in the MACHO bulge fields, there may
be ~250 RCB stars in the reddened "exclusion" zone toward the bulge.Comment: 16 pages, 5 figures, AJ in press High resolution versions of Figures
1 and 2 can be downloaded from
http://morpheus.phys.lsu.edu/~gclayton/figs.pdf (more typos corrected
Building Classroom and Organizational Structure Around Positive Cultural Values
The Compass Project is a self-formed group of graduate and undergraduate
students in the physical sciences at UC Berkeley. Our goals are to improve
undergraduate physics education, provide opportunities for professional
development, and increase retention of students-especially those from
populations typically underrepresented in the physical sciences. Compass
fosters a diverse, collaborative student community by providing a wide range of
services, including a summer program and fall/spring seminar courses. We
describe Compass's cultural values, discuss how community members are
introduced to and help shape those values, and demonstrate how a single set of
values informs the structure of both our classroom and organization.We
emphasize that all members of the Compass community participate in, and benefit
from, our cultural values, regardless of status as student, teacher, or
otherwise.Comment: 4 pages, to be submitted to PERC 2012 proceeding
Discovery of Bright Galactic R Coronae Borealis and DY Persei Variables: Rare Gems Mined from ACVS
We present the results of a machine-learning (ML) based search for new R
Coronae Borealis (RCB) stars and DY Persei-like stars (DYPers) in the Galaxy
using cataloged light curves from the All-Sky Automated Survey (ASAS) Catalog
of Variable Stars (ACVS). RCB stars - a rare class of hydrogen-deficient
carbon-rich supergiants - are of great interest owing to the insights they can
provide on the late stages of stellar evolution. DYPers are possibly the
low-temperature, low-luminosity analogs to the RCB phenomenon, though
additional examples are needed to fully establish this connection. While RCB
stars and DYPers are traditionally identified by epochs of extreme dimming that
occur without regularity, the ML search framework more fully captures the
richness and diversity of their photometric behavior. We demonstrate that our
ML method can use newly discovered RCB stars to identify additional candidates
within the same data set. Our search yields 15 candidates that we consider
likely RCB stars/DYPers: new spectroscopic observations confirm that four of
these candidates are RCB stars and four are DYPers. Our discovery of four new
DYPers increases the number of known Galactic DYPers from two to six;
noteworthy is that one of the new DYPers has a measured parallax and is m ~ 7
mag, making it the brightest known DYPer to date. Future observations of these
new DYPers should prove instrumental in establishing the RCB connection. We
consider these results, derived from a machine-learned probabilistic
classification catalog, as an important proof-of-concept for the efficient
discovery of rare sources with time-domain surveys.Comment: 18 pages, 2 new figures, accepted for publication in Ap
New Magellanic Cloud R Coronae Borealis and DY Per type stars from the EROS-2 database: the connection between RCBs, DYPers and ordinary carbon stars
R Coronae Borealis stars (RCB) are a rare type of evolved carbon-rich
supergiant stars that are increasingly thought to result from the merger of two
white dwarfs, called the Double degenerate scenario. This scenario is also
studied as a source, at higher mass, of type Ia Supernovae (SnIa) explosions.
Therefore a better understanding of RCBs composition would help to constrain
simulations of such events. We searched for and studied RCB stars in the EROS
Magellanic Clouds database. We also extended our research to DY Per type stars
(DYPers) that are expected to be cooler RCBs (T~3500 K) and much more numerous
than their hotter counterparts. The light curves of ~70 millions stars have
been analysed to search for the main signature of RCBs and DYPers: a large drop
in luminosity. Follow-up optical spectroscopy was used to confirm each
photometric candidate found. We have discovered and confirmed 6 new Magellanic
Cloud RCB stars and 7 new DYPers, but also listed new candidates: 3 RCBs and 14
DYPers. We estimated a range of Magellanic RCB shell temperatures between 360
and 600 K. We confirm the wide range of absolute luminosity known for RCB
stars, M_V~-5.2 to -2.6. Our study further shows that mid-infrared surveys are
ideal to search for RCB stars, since they have thinner and cooler circumstellar
shells than classical post-AGB stars. In addition, by increasing the number of
known DYPers by ~400%, we have been able to shed light on the similarities in
the spectral energy distribution between DYPers and ordinary carbon stars. We
also observed that DYPer circumstellar shells are fainter and hotter than those
of RCBs. This suggests that DYPers may simply be ordinary carbon stars with
ejection events, but more abundance analysis is necessary to give a status on a
possible evolutionnary connexion between RCBs and DYPers.Comment: 22 pages, 38 figures, Accepted for publication in A&
R Coronae Borealis stars in the Galactic Bulge discovered by EROS-2
Rare types of variable star may give unique insight into short-lived stages
of stellar evolution. The systematic monitoring of millions of stars and
advanced light curve analysis techniques of microlensing surveys make them
ideal for discovering also such rare variable stars. One example is the R
Coronae Borealis (RCB) stars, a rare type of evolved carbon-rich supergiant. We
have conducted a systematic search of the EROS-2 database for the Galactic
catalogue Bulge and spiral arms to find Galactic RCB stars. The light curves of
100 million stars, monitored for 6.7 years (from July 1996 to February
2003), have been analysed to search for the main signature of RCB stars, large
and rapid drops in luminosity. Follow-up spectroscopy has been used to confirm
the photometric candidates. We have discovered 14 new RCB stars, all in the
direction of the Galactic Bulge, bringing the total number of confirmed
Galactic RCB stars to about 51. After reddening correction, the colours and
absolute magnitudes of at least 9 of the stars are similar to those of
Magellanic RCB stars. This suggests that these stars are in fact located in the
Galactic Bulge, making them the first RCB stars discovered in the Bulge. The
localisation of the 5 remaining RCBs is more uncertain: 4 are either located
behind the Bulge at an estimated maximum distance of 14 kpc or have an unusual
thick circumstellar shell; the other is a DY Per RCB which may be located in
the Bulge, even if it is fainter than the known Magellanic DY Per. From the
small scale height found using the 9 new Bulge RCBs,
pc (95% C.L.), we conclude that the RCB stars follow a disk-like distribution
inside the Bulge.Comment: 20 pages, 26 figures, Accepted in A&
Eu-Social Science: The Role of Internet Social Networks in the Collection of Bee Biodiversity Data
Background
Monitoring change in species diversity, community composition and phenology is vital to assess the impacts of anthropogenic activity and natural change. However, monitoring by trained scientists is time consuming and expensive.
Methodology/Principal Findings
Using social networks, we assess whether it is possible to obtain accurate data on bee distribution across the UK from photographic records submitted by untrained members of the public, and if these data are in sufficient quantity for ecological studies. We used Flickr and Facebook as social networks and Flickr for the storage of photographs and associated data on date, time and location linked to them. Within six weeks, the number of pictures uploaded to the Flickr BeeID group exceeded 200. Geographic coverage was excellent; the distribution of photographs covered most of the British Isles, from the south coast of England to the Highlands of Scotland. However, only 59% of photographs were properly uploaded according to instructions, with vital information such as âtagsâ or location information missing from the remainder. Nevertheless, this incorporation of information on location of photographs was much higher than general usage on Flickr (âŒ13%), indicating the need for dedicated projects to collect spatial ecological data. Furthermore, we found identification of bees is not possible from all photographs, especially those excluding lower abdomen detail. This suggests that giving details regarding specific anatomical features to include on photographs would be useful to maximise success.
Conclusions/Significance
The study demonstrates the power of social network sites to generate public interest in a project and details the advantages of using a group within an existing popular social network site over a traditional (specifically-designed) web-based or paper-based submission process. Some advantages include the ability to network with other individuals or groups with similar interests, and thus increasing the size of the dataset and participation in the project
The Dust Properties of Two Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: in Search of a Possible Link
We present new Spitzer/IRS spectra of two hot R Coronae Borealis (RCB) stars,
one in the Galaxy,V348 Sgr, and one lying in the LMC, HV 2671. These two
objects may constitute a link between the RCB stars and the late Wolf-Rayet
([WCL]) class of central stars of planetary nebula (CSPNe) such as CPD -56 8032
that has little or no hydrogen in their atmospheres. HV 2671 and V348 Sgr are
members of a rare subclass that has significantly higher effective temperatures
than most RCB stars, but sharing the traits of hydrogen deficiency and dust
formation that define the cooler RCB stars. The [WC] CSPNe star, CPD -56 8032,
displays evidence for dual-dust chemistry showing both PAHs and crystalline
silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but shows
no sign of having crystalline silicates. The spectrum of V348 Sgr is very
different from those of CPD -56 8032 and HV 2671. The PAH emission seen
strongly in the other two stars is not present. Instead, the spectrum is
dominated by a broad emission centered at about 8.2 micron. The mid-IR spectrum
of CPD -56 8032 shows emission features that may be associated with C60. The
other two stars do not show evidence for C60. HV 2671 has also been detected by
Herschel/PACS and SPIRE. V348 Sgr and CPD -56 8032 have been detected by
AKARI/FIS. These data were combined with Spitzer, IRAS, 2MASS and other
photometry to produce their spectral energy distributions from the visible to
the far-IR. Monte Carlo radiative transfer modeling was used to study the
circumstellar dust around these stars. HV 2671 and CPD -56 8032 require both a
flared inner disk with warm dust and an extended diffuse envelope with cold
dust to to fit their SEDs. The SED of V348 Sgr can be fit with a much smaller
disk and envelope.Comment: 20 pages, 5 figures, accepted for publication in The Astronomical
Journa
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