722 research outputs found
Multiperiodicity in the newly discovered mid-late Be star V2104 Cygni
We obtained the first long, homogenous time-series of V2104Cyg, consisting of
679 datapoints, with the uvbybeta photometers of Sierra Nevada and San Pedro
Martir Observatories with the aim to detect and subsequently interpret the
intrinsic frequencies of this previously unstudied variable star, which turned
out to be a Be star. We try to figure out its place among the variable B stars
on the upper Main Sequence. In order to obtain additional information on
physical parameters we collected a few spectra with the ELODIE and FIES
instruments. We searched for frequencies in the uvby passbands using 2
different frequency analysis methods and used the S/N>4 criterion to select the
significant periodicities. We obtained an estimate of the physical parameters
of the underlying B star of spectral type between B5 and B7, by correcting for
the presence of a circumstellar disk, using a formalism based on the strenght
of the Halpha line emission. We detected 3 independent frequencies with
amplitudes below 0.01mag, f1 = 4.7126 c/d, f2 = 2.2342 c/d and f3 = 4.671 c/d,
and discovered that V2104Cyg is a Be star. The fast rotation (vsini=290+/-10
km/s, and 27<i<45) hampered the investigation of the associated pulsational
parameters l. Nevertheless, the most plausible explanation for the observed
variability of this mid-late type Be star is a non-radial pulsation model. This
paper is based on observations obtained at the Observatorio Astronomico
Nacional San Pedro Martir (Mexico), Observatorio de Sierra Nevada (Spain),
Observatoire de Haute Provence (France), and on observations made with the
Nordic Optical Telescope, Observatorio Roque de los Muchachos, La Palma, Spain.Comment: 7 pages, 4 figures, A&A accepte
Enlarging conference learning : at the crossroads of fat studies and conference pedagogies
This article stages an encounter between the field of fat studies and conference pedagogy scholarship. After laying the foundations for a reading of academic conferences as learning spaces, the authors present two examples—International Fat Studies Conferences held in Aotearoa, New Zealand, in 2012 and 2016—to unpack these ideas. The framing of fat studies conferences as pedagogical spaces sparks questions that travel in multiple directions. It calls us to consider possible modifications to the design of fat studies conferences, as well as how discussions about fat pedagogy may have a wider application to academic gatherings
Dynamical evolution of titanium, strontium, and yttrium spots on the surface of the HgMn star HD 11753
Aims. We gathered about 100 high-resolution spectra of three typical HgMn
(mercury-manganese) stars, HD 11753, HD 53244, and HD 221507, to search for
slowly pulsating B-like pulsations and surface inhomogeneous distribution of
various chemical elements. Methods. Classical frequency analysis methods were
used to detect line profile variability and to determine the variation period.
Doppler imaging reconstruction was performed to obtain abundance maps of
chemical elements on the stellar surface. Results. For HD 11753, which is the
star with the most pronounced variability, distinct spectral line profile
changes were detected for Ti, Sr, Y, Zr, and Hg, whereas for HD 53244 and HD
221507 the most variable line profiles belong to the elements Hg and Y,
respectively. We derived rotation periods for all three stars from the
variations of radial velocities and equivalent widths of spectral lines
belonging to inhomogeneously distributed elements: P_rot (HD 11753)=9.54 d,
P_rot (HD 53244)=6.16 d, and P_rot (HD 221507)=1.93 d. For HD 11753 the Doppler
imaging technique was applied to derive the distribution of the most variable
elements Ti, Sr, and Y using two datasets separated by ~65 days. Results of
Doppler imaging reconstruction revealed noticeable changes in the surface
distributions of TiII, SrII, and YII between the datasets, indicating the
hitherto not well understood physical processes in stars with radiative
envelopes that cause a rather fast dynamical chemical spot evolution.Comment: Accepted for publication in Astronomy and Astrophysics, 6 pages, 9
figures, 2 tables
KIC 4768731: a bright long-period roAp star in theKeplerfield
We report the identification of 61.45 d−1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of Teff = 8100 ± 200 K, log g = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i = 14.8 ± 1.6 km s−1.
Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teff and log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr
Salinity dynamics under different water management plans coupled with sea level rise scenarios in the Red River Delta, Vietnam
In recent years, saltwater intrusion in river estuaries has become more severe and frequent worldwide. The common reasons lie in increasing freshwater withdrawal, river flow regulation and sea level rise due to global warming. In particular, the Red River Delta in northern Vietnam is facing a strong population growth worsening the pressure on freshwater resources for drinking water and irrigation needs. During the dry season, increasing conflicts and constraints in freshwater availability have already been experienced. Adverse combinations of river flow regulations and high sea levels lead to severe upstream propagations of salinity. This study takes advantage of a statistical characterization of discharges released from Hoa Binh reservoir and observed at Son Tay station, the main river flow control upstream of the river delta, along with downscaled and updated sea level rise sce- narios to estimate the future extents of saltwater intrusion under different options of water release from reser- voirs in the dry season. To do so, a 1D hydraulic model of the river delta network was implemented using MIKE11 software. The hydraulic and the quality modules were calibrated and validated with respect to the present scenario by using water stages and salinity concentrations observed in estuary branches. Sea level rise projections for 2050 and 2100 referred to RCP4.5 and RCP8.5 AR5 emission scenarios were then considered. Results show that river flow regulation can provide an effective mitigation measure. A 20–30% increase in the discharge released from the Son Tay station would be beneficial to push downstream the saltwater intrusion in the main Red River branch during the dry season. For instance, in 2050 the 1‰ salt concentration front is ex- pected to be pushed back at least 6 km when the exceeding probability of the discharge released by Son Tay station decreases from 95% to 25%
Spectroscopic Survey of {\gamma} Doradus Stars I. Comprehensive atmospheric parameters and abundance analysis of {\gamma} Doradus stars
We present a spectroscopic survey of known and candidate \,Doradus
stars. The high-resolution, high signal-to-noise spectra of 52 objects were
collected by five different spectrographs. The spectral classification,
atmospheric parameters (\teff, , ), and chemical
composition of the stars were derived. The stellar spectral and luminosity
classes were found between G0-A7 and IV-V, respectively. The initial values for
\teff\ and \logg\ were determined from the photometric indices and spectral
energy distribution. Those parameters were improved by the analysis of hydrogen
lines. The final values of \teff, \logg\ and were derived from the iron
lines analysis. The \teff\ values were found between 6000\,K and 7900\,K, while
\logg\,values range from 3.8 to 4.5\,dex. Chemical abundances and
values were derived by the spectrum synthesis method. The values were
found between 5 and 240\,km\,s. The chemical abundance pattern of
\,Doradus stars were compared with the pattern of non-pulsating stars.
It turned out that there is no significant difference in abundance patterns
between these two groups. Additionally, the relations between the atmospheric
parameters and the pulsation quantities were checked. A strong correlation
between the and the pulsation periods of \,Doradus variables
was obtained. The accurate positions of the analysed stars in the H-R diagram
have been shown. Most of our objects are located inside or close to the blue
edge of the theoretical instability strip of \,Doradus.Comment: 18 pages, 13 figure
Paper Session I-A - Modeling Current and Future Launch Vehicle Processing Using Object-Oriented Simulation Techniques
STARSIM, an acronym for Space Transportation Activities and Resources Simulation, is an objectoriented, menu-driven, user-friendly, decision support system for simulating National Space Transportation System (NSTS) processing, as well as Personnel Launch System (PLS)-National Launch System (NLS), PLS-Proton, PLS-Titan IV, Hermes-Ariane 5 and Cargo Transfer Return Vehicle (CTRV) processing. For each launch system modeled, output is displayed numerically (for global statistical information), in pie chart form (to visualize percentages of subcategories associated with a main category) and in Gantt chart form (for visualizing when and where each launch vehicle experiences waiting, processing, blocking and maintenance periods, and the reasons for blocking). Users may input a comprehensive set of system parameters (e.g., number of launch vehicles, processing times at each facility, number of bays at a particular facility) using a window-based environment, or by supplying an existing input data file. Data for existing launch systems and representative data for proposed systems are used to illustrate output for the models mentioned above. The object-oriented methodology employed in the initial model (i.e., NSTS processing) permitted additional models to be implemented in a minimum amount of time and effort
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