397 research outputs found
Halo Velocity Groups in the Pisces Overdensity
We report spectroscopic observations with the Gemini South Telescope of 5
faint V~20 RR Lyrae stars associated with the Pisces overdensity. At a
heliocentric and galactocentric distance of ~80 kpc, this is the most distant
substructure in the Galactic halo known to date. We combined our observations
with literature data and confirmed that the substructure is composed of two
different kinematic groups. The main group contains 8 stars and has =
50 km/s, while the second group contains four stars at a velocity of
= -52 km/s, where V_{gsr} is the radial velocity in the galactocentric standard
of rest. The metallicity distribution of RR Lyrae stars in the Pisces
overdensity is centered on [Fe/H]=-1.5 dex and has a width of 0.3 dex. The new
data allowed us to establish that both groups are spatially extended making it
very unlikely that they are bound systems, and are more likely to be debris of
a tidally disrupted galaxy or galaxies. Due to small sky coverage, it is still
unclear whether these groups have the same or different progenitors.Comment: 21 pages, 5 figures, 3 tables, accepted to Astrophysical Journa
Time Variability of Quasars: the Structure Function Variance
Significant progress in the description of quasar variability has been
recently made by employing SDSS and POSS data. Common to most studies is a
fundamental assumption that photometric observations at two epochs for a large
number of quasars will reveal the same statistical properties as well-sampled
light curves for individual objects. We critically test this assumption using
light curves for a sample of 2,600 spectroscopically confirmed quasars
observed about 50 times on average over 8 years by the SDSS stripe 82 survey.
We find that the dependence of the mean structure function computed for
individual quasars on luminosity, rest-frame wavelength and time is
qualitatively and quantitatively similar to the behavior of the structure
function derived from two-epoch observations of a much larger sample. We also
reproduce the result that the variability properties of radio and X-ray
selected subsamples are different. However, the scatter of the variability
structure function for fixed values of luminosity, rest-frame wavelength and
time is similar to the scatter induced by the variance of these quantities in
the analyzed sample. Hence, our results suggest that, although the statistical
properties of quasar variability inferred using two-epoch data capture some
underlying physics, there is significant additional information that can be
extracted from well-sampled light curves for individual objects.Comment: Presented at the "Classification and Discovery in Large Astronomical
Surveys" meeting, Ringberg Castle, 14-17 October, 200
Quasar Selection Based on Photometric Variability
We develop a method for separating quasars from other variable point sources
using SDSS Stripe 82 light curve data for ~10,000 variable objects. To
statistically describe quasar variability, we use a damped random walk model
parametrized by a damping time scale, tau, and an asymptotic amplitude
(structure function), SF_inf. With the aid of an SDSS spectroscopically
confirmed quasar sample, we demonstrate that variability selection in typical
extragalactic fields with low stellar density can deliver complete samples with
reasonable purity (or efficiency, E). Compared to a selection method based
solely on the slope of the structure function, the inclusion of the tau
information boosts E from 60% to 75% while maintaining a highly complete sample
(98%) even in the absence of color information. For a completeness of C=90%, E
is boosted from 80% to 85%. Conversely, C improves from 90% to 97% while
maintaining E=80% when imposing a lower limit on tau. With the aid of color
selection, the purity can be further boosted to 96%, with C= 93%. Hence,
selection methods based on variability will play an important role in the
selection of quasars with data provided by upcoming large sky surveys, such as
Pan-STARRS and the Large Synoptic Survey Telescope (LSST). For a typical
(simulated) LSST cadence over 10 years and a photometric accuracy of 0.03 mag
(achieved at i~22), C is expected to be 88% for a simple sample selection
criterion of tau>100 days. In summary, given an adequate survey cadence,
photometric variability provides an even better method than color selection for
separating quasars from stars.Comment: (v2) 50 pages, accepted to Ap
A re-interpretation of the Triangulum-Andromeda stellar clouds: a population of halo stars kicked out of the Galactic disk
The Triangulum-Andromeda stellar clouds (TriAnd1 and TriAnd2) are a pair of
concentric ring- or shell-like over-densities at large ( 30 kpc)
and ( -10 kpc) in the Galactic halo that are thought to have been
formed from the accretion and disruption of a satellite galaxy. This paper
critically re-examines this formation scenario by comparing the number ratio of
RR Lyrae to M giant stars associated with the TriAnd clouds with other
structures in the Galaxy. The current data suggest a stellar population for
these over-densities ( at 95% confidence) quite unlike
any of the known satellites of the Milky Way ( for
the very largest and for the smaller satellites) and more
like the population of stars born in the much deeper potential well inhabited
by the Galactic disk (). N-body simulations of a
Milky-Way-like galaxy perturbed by the impact of a dwarf galaxy demonstrate
that, in the right circumstances, concentric rings propagating outwards from
that Galactic disk can plausibly produce similar over-densities. These results
provide dramatic support for the recent proposal by Xu et al. (2015) that,
rather than stars accreted from other galaxies, the TriAnd clouds could
represent stars kicked-out from our own disk. If so, these would be the first
populations of disk stars to be found in the Galactic halo and a clear
signature of the importance of this second formation mechanism for stellar
halos more generally. Moreover, their existence at the very extremities of the
disk places strong constraints on the nature of the interaction that formed
them.Comment: 27 pages, 8 figures; published in MNRA
The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility
RR Lyr stars are ideal massless tracers that can be used to study the total
mass and dark matter content of the outer halo of the Milky Way. This is
because they are easy to find in the light curve databases of large stellar
surveys and their distances can be determined with only knowledge of the light
curve. We present here a sample of 112 RR Lyr beyond 50 kpc in the outer halo
of the Milky Way, excluding the Sgr streams, for which we have obtained
moderate resolution spectra with Deimos on the Keck 2 Telescope. Four of these
have distances exceeding 100 kpc. These were selected from a much larger set of
447 candidate RR Lyr which were datamined using machine learning techniques
applied to the light curves of variable stars in the Palomar Transient Facility
database. The observed radial velocities taken at the phase of the variable
corresponding to the time of observation were converted to systemic radial
velocities in the Galactic standard of rest. From our sample of 112 RR Lyr we
determine the radial velocity dispersion in the outer halo of the Milky Way to
be ~90 km/s at 50 kpc falling to about 65 km/s near 100 kpc once a small number
of major outliers are removed. With reasonable estimates of the completeness of
our sample of 447 candidates and assuming a spherical halo, we find that the
stellar density in the outer halo declines as the -4 power of r.Comment: Accepted for publication in the Ap
Cultural Appropriation of Polynesian Portrayed In Moana Movie
This research aims to identify and describe cultural appropriation that were found in Moana. Cultural appropriation is one of the negative actions that can harm one culture. This action generally occurs due to a lack of understanding and appreciation of a culture. Based on Rogers[6] cultural appropriation as the use of a culture's symbols, artifacts, genres, rituals, or technologies by members of another culture, is inescapable when cultures come into contact, including virtual or representational contact. Rogers also divided cultural appropriation into four types, there are cultural exchange, cultural dominance, cultural exploitation, and transculturation. Based on Rogers theory above, cultural appropriation that were found in Moana is cultural exploitation. This research was used Qualitative descriptive method. The source data of this research are from āMoanaā by Ron Clements and John Musker. This movie was released in 2016 with 113 minutes duration. This analysis shows there are four points of cultural appropriation that were found in āMoanaā. Firstly, depiction figure of āMauiā, a demigod figure illustrated very different from the original form in the movie Moana. Secondly, depiction of Kakamora people. Thirdly, depiction of the clichĆ© coconuts. Fourthly, Disney removing Mauiās family out of the tale. This leads to deviations in views towards the representatives of the population and Polynesian beliefs
KEANEKARAGAMAN JENIS ANGGREK ALAM (Orchidaceae) BERDASARKAN KETINGGIAN TEMPAT DI GUNUNG POTENG CAGAR ALAM RAYA PASI KOTA SINGKAWANG PROVINSI KALIMANTAN BARAT
Natural orchids are one of the flora in Mount Poteng which is included of Raya Pasi Nature Reserve located at Singkawang City, West Kalimantan Province. Orchids have economic value for source of income and be beneficial to ecology that needs to be protected. The altitudes and environmental factors strongly affected the presence of orchid species.The research aims to record the diversity of natural orchids species based on the altitudes place in Mount Poteng. The research was conducted on February 28 until March 28, 2020. This research uses survey method. The research sample was taken using double plots method and to determine sample plots locations is conducted by purposive. The total number of the sample plots is 16 plots and each plot measure 20 by 50 meters. Based on the result of research found 19 species of natural orchids that consist of 348 individuals. The results analysis of the diversity index of orchid species in whole of altitudes at Mount Poteng is 1,338 that is included medium range. The highest species diversity index of 1,300 occurred at altitude of 400-500 m asl and the lowest species diversity index at altitude of 700-725 m asl that is 0,594. Orchid species which found in whole of altitudes is Dendrobium crumenatum. Furthermor, there were found the orchid species on certain heights are Cleisostoma scortechinii, Cordiglottis filiformis, Ludisia discolor, and Phalaenopsis pantherina at altitude of 400-500 m asl and species of Bromheadia finlaysoniana and Pomatocalpa latifolia found at altitude of 700-725 m asl.Keywords: altitudes, mount poteng, orchids, species diversit
Connecting the Milky Way potential profile to the orbital timescales and spatial structure of the Sagittarius Stream
Recent maps of the halo using RR Lyrae from Pan-STARRS1 have clearly depicted
the spatial structure of the Sagittarius stream. These maps show the leading
and trailing stream apocenters differ in galactocentric radius by a factor of
two, and also resolve substructure in the stream at these apocenters. Here we
present dynamical models that reproduce these features of the stream in simple
Galactic potentials. We find that debris at the apocenters must be dynamically
young, in the sense of being stripped off in the last two pericentric passages,
while the Sagittarius dwarf is currently experiencing a third passage. The
ratio of apocenters is sensitive to both dynamical friction and the outer slope
of the Galactic rotation curve. These dependences can be understood with simple
regularities connecting the apocentric radii, circular velocities, and orbital
period of the progenitor. The effect of dynamical friction on the stream can be
constrained using substructure within the leading apocenter. Our ensembles of
models are not intended as statistically proper fits to the stream.
Nevertheless, out of the range of models we consider, we consistently find the
mass within 100 kpc to be , with a nearly
flat rotation curve between 50 and 100 kpc. This points to a more extended
Galactic halo than assumed in some current models. As in previous work, we find
prolate or triaxial halos ease agreement with the track of the leading stream.
We display the behavior of our models in various observational spaces and
characterize the substructure expected within the stream. In particular, the
young trailing stream visible near trailing apocenter should exhibit a tight
trend of velocity with distance separate from the older debris, and we suggest
that this will serve as an especially useful probe of the outer Galactic
potential.Comment: Submitted to MNRA
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