57 research outputs found
Constraining dark photon model with dark matter from CMB spectral distortions
Many extensions of Standard Model (SM) include a dark sector which can
interact with the SM sector via a light mediator. We explore the possibilities
to probe such a dark sector by studying the distortion of the CMB spectrum from
the blackbody shape due to the elastic scatterings between the dark matter and
baryons through a hidden light mediator. We in particular focus on the model
where the dark sector gauge boson kinetically mixes with the SM and present the
future experimental prospect for a PIXIE-like experiment along with its
comparison to the existing bounds from complementary terrestrial experiments.Comment: 6 pages, 8 figure
Searching for Axino-Like Particle at Fixed Target Experiments
We investigate the detectability of axino-like particle, which is defined as
a supersymmetric partner of axion-like particle and can be a good candidate for
dark matter in our Universe. Especially, we consider the fixed target
experiments to search for the light axino-like particle with a neutralino as
the next-to-lightest supersymmetric particle. We calculate the production and
decay rate of neutralinos and the consequent number of events (such as photons
and charged leptons) that are produced when the neutralinos decay to the
axino-like particles.Comment: 10 pages, 7 figures, Published in Physics of the Dark Univers
Introducing Murine Microbiome Database (MMDB): A Curated Database with Taxonomic Profiling of the Healthy Mouse Gastrointestinal Microbiome
The gut microbiota modulates overall metabolism, the immune system and brain development of the host. The majority of mammalian gut microbiota consists of bacteria. Among various model animals, the mouse has been most widely used in pre-clinical biological experiments. The significant compositional differences in taxonomic profiles among different mouse strains due to gastrointestinal locations, genotypes and vendors have been well documented. However, details of such variations are yet to be elucidated. This study compiled and analyzed 16S rRNA gene-based taxonomic profiles of 554 healthy mouse samples from 14 different projects to construct a comprehensive database of the microbiome of a healthy mouse gastrointestinal tract. The database, named Murine Microbiome Database, should provide researchers with useful taxonomic information and better biological insight about how each taxon, such as genus and species, is associated with locations in the gastrointestinal tract, genotypes and vendors. The database is freely accessible over the Internet.
Precise Radial Velocities of Polaris: Detection of Amplitude Growth
We present a first results from a long-term program of a radial velocity
study of Cepheid Polaris (F7 Ib) aimed to find amplitude and period of
pulsations and nature of secondary periodicities. 264 new precise radial
velocity measurements were obtained during 2004-2007 with the fiber-fed echelle
spectrograph Bohyunsan Observatory Echelle Spectrograph (BOES) of 1.8m
telescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We find a
pulsational radial velocity amplitude and period of Polaris for three seasons
of 2005.183, 2006.360, and 2007.349 as 2K = 2.210 +/- 0.048 km/s, 2K = 2.080
+/- 0.042 km/s, and 2K = 2.406 +/- 0.018 km/s respectively, indicating that the
pulsational amplitudes of Polaris that had decayed during the last century is
now increasing rapidly. The pulsational period was found to be increasing too.
This is the first detection of a historical turnaround of pulsational amplitude
change in Cepheids. We clearly find the presence of additional radial velocity
variations on a time scale of about 119 days and an amplitude of about +/- 138
m/s, that is quasi-periodic rather than strictly periodic. We do not confirm
the presence in our data the variation on a time scale 34-45 days found in
earlier radial velocity data obtained in 80's and 90's. We assume that both the
119 day quasi-periodic, noncoherent variations found in our data as well as
34-45 day variations found before can be caused by the 119 day rotation periods
of Polaris and by surface inhomogeneities such as single or multiple spot
configuration varying with the time.Comment: 15 pages, 7 figures, Accepted for publication in The Astronomical
Journa
A search for exoplanets around north circumpolar stars. VII. Detection of planetary companion orbiting the largest host star HD 18438
We have been conducting a exoplanet search survey using Bohyunsan Observatory
Echelle Spectrograph (BOES) for the last 18 years. We present the detection of
exoplanet candidate in orbit around HD 18438 from high-precision radial
velocity (RV) mesurements. The target was already reported in 2018 (Bang et al.
2018). They conclude that the RV variations with a period of 719 days are
likely to be caused by the pulsations because the Lomb-Scargle periodogram of
HIPPARCOS photometric and Ha EW variations for HD 18438 show peaks with periods
close to that of RV variations and there were no correlations between bisectors
and RV measurements. However, the data were not sufficient to reach a firm
conclusion. We obtained more RV data for four years. The longer time baseline
yields a more accurate determination with a revised period of 803 +/- 5 days
and the planetary origin of RV variations with a minimum planetary companion
mass of 21 +/- 1 MJup. Our current estimate of the stellar parameters for HD
18438 makes it currently the largest star with a planetary companion.Comment: 6 pages, 4 figures, Accept to the Journal of the Korean Astronomical
Societ
Hybrid star HD 81817 accompanied by brown dwarf or substellar companion
HD 81817 is known as a hybrid star. Hybrid stars have both cool stellar wind
properties and Ultraviolet (UV) or even X-ray emission features of highly
ionized atoms in their spectra. A white dwarf companion has been suggested as
the source of UV or X-ray features. HD 81817 has been observed since 2004 as a
part of a radial velocity (RV) survey program to search for exoplanets around K
giant stars using the Bohyunsan Observatory Echelle Spectrograph at the 1.8 m
telescope of Bohyunsan Optical Astronomy Observatory in Korea. We obtained 85
RV measurements between 2004 and 2019 for HD 81817 and found two periodic RV
variations. The amplitudes of RV variations are around 200 m s^-1, which are
significantly lower than that expected from a closely orbiting white dwarf
companion. Photometric data and relevant spectral lines were also analyzed to
help determine the origin of the periodic RV variations. We conclude that
627.4-day RV variations are caused by intrinsic stellar activities such as
long-term pulsations or rotational modulations of surface activities based on
H{\alpha} equivalent width (EW) variations of a similar period. On the other
hand, 1047.1-day periodic RV variations are likely to be caused by a brown
dwarf or substellar companion, which is corroborated by a recent GAIA proper
motion anomaly for HD 81817. The Keplerian fit yields a minimum mass of 27.1
M_Jup, a semimajor axis of 3.3 AU, and an eccentricity of 0.17 for the stellar
mass of 4.3 M_sun for HD 81817. The inferred mass puts HD 81817 b in the brown
dwarf desert
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