785 research outputs found
Be Stars in the Open Cluster NGC 6830
We report the discovery of 2 new Be stars, and re-identify one known Be star
in the open cluster NGC 6830. Eleven H-alpha emitters were discovered using the
H-alpha imaging photometry of the Palomar Transient Factory Survey. Stellar
membership of the candidates was verified with photometric and kinematic
information using 2MASS data and proper motions. The spectroscopic confirmation
was carried out by using the Shane 3-m telescope at Lick observatory. Based on
their spectral types, three H-alpha emitters were confirmed as Be stars with
H-alpha equivalent widths > -10 Angstrom. Two objects were also observed by the
new spectrograph SED-Machine on the Palomar 60 inch Telescope. The SED-Machine
results show strong H-alpha emission lines, which are consistent with the
results of the Lick observations. The high efficiency of the SED-Machine can
provide rapid observations for Be stars in a comprehensive survey in the
future.Comment: 11 pages, 8 figures, AJ in pres
The Information Of The Milky Way From 2MASS Whole Sky Star Count: The Bimodal Color Distributions
The J-Ks color distribution (CD) with a bin size of 0.05 magnitude for the
entire Milky Way has been carried out by using the Two Micron All Sky Survey
Point Source Catalog (2MASS PSC). The CDs are bimodal, which has a red peak at
0.8 < J-Ks < 0.85 and a blue peak at 0.3 < J-Ks < 0.4. The colors of the red
peak are more or less the same for the whole sky, but that of the blue peak
depend on Galactic latitude, (J-Ks ~ 0.35 at low Galactic latitudes and 0.35 <
J-Ks < 0.4 for other sky areas). The blue peak dominates the bimodal CDs at low
Galactic latitudes and becomes comparable with the red peak in other sky
regions. In order to explain the bimodal distribution and the global trend
shown by the all sky 2MASS CDs, we assemble an empirical HR diagram, which is
composed by observational-based near infrared HR diagrams and color magnitude
diagrams, and incorporate a Milky Way model. In the empirical HR diagram, the
main sequence stars turnoff the thin disk is relatively bluer, (J-Ks)0 = 0.31,
when we compare with the thick disk which is (J-Ks)0 = 0.39. The age of the
thin/thick disk is roughly estimated to be around 4-5/8-9 Gyr according to the
color-age relation of the main sequence turnoff. In general, the 2MASS CDs can
be treated as a tool to census the age of stellar population of the Milky Way
in a statistical manner and to our knowledge this is a first attempt to measure
the age.Comment: Accepted by ApJ on Sept. 11 201
Discovery of a New Member of the Inner Oort Cloud from The Next Generation Virgo Cluster Survey
We report the discovery of 2010 GB, a likely new member of the Inner
Oort Cloud (IOC). 2010 GB is one of 91 Trans Neptunian Objects (TNOs)
and Centaurs discovered in a 76 deg contiguous region imaged as part of the
Next Generation Virgo Cluster Survey (NGVS) --- a moderate ecliptic latitude
survey reaching a mean limiting magnitude of --- using
MegaPrime on the 3.6m Canada France Hawaii Telescope. 2010 GB is found
to have an orbit with semi-major axis AU, inclination and pericentre AU. This is the second largest
perihelion distance among known solar system objects. Based on the sky coverage
and depth of the NGVS, we estimate the number of IOC members with sizes larger
than 300 km ( mag) to be . A comparison of the
detection rate from the NGVS and the PDSSS (a characterized survey that
`re-discovered' the IOC object Sedna) gives, for an assumed a power-law LF for
IOC objects, a slope of , with only two detections
in this region this slope estimate is highly uncertain.Comment: 20 pages, 3 figures, 1 table. Accepted for publication in The
Astrophysical Journal Letter
Asymmetric Exchange Rate Exposure and Industry Characteristics : Evidence from Japanese Data
This paper investigates the asymmetric effects of exchange rate exposure on Japanese stock returns at the industry level.Using the asymmetric correlation test of Hong et al.(2007), we examine five major currencies against the yen and thirty-three Japanese sectoral stock returns.Signi ficant asymmetric responses in stock returns to exchange rate changes are found in the pharmaceutical, real estate, and air transportation industries.These findings are consistent with the pricing-to-market and hysteretic behavior for the pharmaceutical and air transportation industries and with the hedging behavior for the real estate industry.The results for the threshold models confirm that the asymmetric exposures are based on industry characteristics.exchange rate exposure, asymmetric correlation, threshold model
TEC enhancement due to energetic electrons above Taiwan and the West Pacific
The energetic electrons of the inner radiation belt during a geomagnetic
disturbance can penetrate in the forbidden range of drift shells located at the
heights of the topside equatorial ionosphere (<1000 km). A good correlation was
previously revealed between positive ionospheric storms and intense fluxes of
quasi-trapped 30-keV electrons at ~900 km height in the forbidden zone. In the
present work, we use statistics to validate an assumption that the intense
electron fluxes in the topside equatorial ionosphere can be an important source
of the ionization in the low-latitude ionosphere. The data on the energetic
electrons were obtained from polar orbiting satellites over the periods of the
62 strong geomagnetic storms from 1999 to 2006. Ionospheric response to the
selected storms was determined using global ionospheric maps of vertical total
electron content (VTEC). A case-event study of a major storm on 9 November 2004
provided experimental evidence in support to the substantial ionization effect
of energetic electrons during positive ionospheric storms at the low latitudes.
Statistical analysis of nine magnetic storms indicated that the VTEC increases
coincided with and coexisted with intense 30-keV electron fluxes irrespective
of local time and phase of geomagnetic storm. We concluded that extremely
intense fluxes of the 30-keV electrons in the topside low-latitude ionosphere
can contribute ~ 10 - 30 TECU to the localized positive ionospheric storms.Comment: 15 pages, 4 figures, 1 table accepted for publication in Terrestrial,
Atmospheric and Oceanic Sciences (TAO), Dec. 2012 A special issue on
"Connection of solar and heliospheric activities with near-Earth space
weather: Sun-Earth connection
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