3,488 research outputs found
A 3D study of the photosphere of HD 99563 - I. Pulsation analysis
We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD 99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar disc. The variations are consistent with a distorted non-radial dipole pulsation mode. We measure a 1.6 km s−1 rotational variation in the mean radial velocities of Hα and argue that this is the first observation of Hα abundance spots caused by He settling through suppression of convection by the magnetic field on an oblique rotator, in support of a prime theory for the excitation mechanism of roAp star pulsation. We demonstrate that HD 99563 is the second roAp star to show aspect dependence of blue-to-red running wave line profile variations in Nd iii spots
Long-term Variability of HCO Masers in Star-forming Regions
We present results of a multi-epoch monitoring program on variability of
6cm formaldehyde (HCO) masers in the massive star forming region
NGC7538IRS1 from 2008 to 2015 conducted with the GBT, WSRT, and
VLA. We found that the similar variability behaviors of the two formaldehyde
maser velocity components in NGC7538IRS1 (which was pointed out by
Araya and collaborators in 2007) have continued. The possibility that the
variability is caused by changes in the maser amplification path in regions
with similar morphology and kinematics is discussed. We also observed
12.2GHz methanol and 22.2GHz water masers toward
NGC7538IRS1. The brightest maser components of CHOH and HO
species show a decrease in flux density as a function of time. The brightest
HCO maser component also shows a decrease in flux density and has a similar
LSR velocity to the brightest HO and 12.2GHz CHOH masers. The line
parameters of radio recombination lines and the 20.17 and 20.97GHz CHOH
transitions in NGC7538IRS1 are also reported. In addition, we
observed five other 6cm formaldehyde maser regions. We found no evidence of
significant variability of the 6cm masers in these regions with respect to
previous observations, the only possible exception being the maser in
G29.960.02. All six sources were also observed in the HCO
isotopologue transition of the 6cm HCO line; HCO absorption
was detected in five of the sources. Estimated column density ratios
[HCO]/[HCO] are reported.Comment: 29 pages, 9 figure
The first evidence for multiple pulsation axes: a new roAp star in the Kepler field, KIC 10195926
We have discovered a new rapidly oscillating Ap star among the Kepler Mission
target stars, KIC 10195926. This star shows two pulsation modes with periods
that are amongst the longest known for roAp stars at 17.1 min and 18.1 min,
indicating that the star is near the terminal age main sequence. The principal
pulsation mode is an oblique dipole mode that shows a rotationally split
frequency septuplet that provides information on the geometry of the mode. The
secondary mode also appears to be a dipole mode with a rotationally split
triplet, but we are able to show within the improved oblique pulsator model
that these two modes cannot have the same axis of pulsation. This is the first
time for any pulsating star that evidence has been found for separate pulsation
axes for different modes. The two modes are separated in frequency by 55
microHz, which we model as the large separation. The star is an alpha^2 CVn
spotted magnetic variable that shows a complex rotational light variation with
a period of Prot = 5.68459 d. For the first time for any spotted magnetic star
of the upper main sequence, we find clear evidence of light variation with a
period of twice the rotation period; i.e. a subharmonic frequency of . We propose that this and other subharmonics are the first observed
manifestation of torsional modes in an roAp star. From high resolution spectra
we determine Teff = 7400 K, log g = 3.6 and v sin i = 21 km/s. We have found a
magnetic pulsation model with fundamental parameters close to these values that
reproduces the rotational variations of the two obliquely pulsating modes with
different pulsation axes. The star shows overabundances of the rare earth
elements, but these are not as extreme as most other roAp stars. The spectrum
is variable with rotation, indicating surface abundance patches.Comment: 17 pages; 16 figures; MNRA
Pulsation in the atmosphere of the roAp star HD 24712. I. Spectroscopic observations and radial velocity measurements
We have investigated the structure of the pulsating atmosphere of one of the
best studied rapidly oscillating Ap stars, HD 24712. For this purpose we
analyzed spectra collected during 2001-2004. An extensive data set was obtained
in 2004 simultaneously with the photometry of the Canadian MOST mini-satellite.
This allows us to connect directly atmospheric dynamics observed as radial
velocity variations with light variations seen in photometry. We directly
derived for the first time and for different chemical elements, respectively
ions, phase shifts between photometric and radial velocity pulsation maxima
indicating, as we suggest, different line formation depths in the atmosphere.
This allowed us to estimate for the first time the propagation velocity of a
pulsation wave in the outer stellar atmosphere of a roAp star to be slightly
lower than the sound speed. We confirm large pulsation amplitudes (150-400 m/s)
for REE lines and the Halpha core, while spectral lines of the other elements
(Mg, Si, Ca, and Fe-peak elements) have nearly constant velocities. We did not
find different pulsation amplitudes and phases for the lines of rare-earth
elements before and after the Balmer jump, which supports the hypothesis of REE
concentration in the upper atmosphere above the hydrogen line-forming layers.
We also discuss radial velocity amplitudes and phases measured for individual
spectral lines as tools for a 3D tomography of the atmosphere of HD 24712.Comment: accepted by A&
Internal Dynamics of the Hypercompact H II Region G28.20-0.04N
High resolution (0.15") Very Large Array observations of 7 mm continuum and
H53a line emission toward the hypercompact H II region G28.20-0.04N reveal the
presence of large-scale ordered motions. We find a velocity gradient of 1000
km/s/pc along the minor axis of the continuum source. Lower resolution
(1.0"-2.3") radio recombination line observations indicate a systematic
increase of line width from H30alpha to H92alpha. Under the assumption that the
H30alpha line does not suffer significant pressure broadening, we have
deconvolved the contributions of statistical broadening (thermal, turbulent,
and pressure) from large-scale motions. The pressure broadening of the
H53alpha, H76alpha, and H92alpha lines implies an electron density of 6.9E+06,
8.5E+05, and 2.8E+05 cm^(-3), respectively.Comment: 12 pages, 2 figures, 1 table, Accepted for publication in Ap
The Early Evolution of Massive Stars: Radio Recombination Line Spectra
Velocity shifts and differential broadening of radio recombination lines are
used to estimate the densities and velocities of the ionized gas in several
hypercompact and ultracompact HII regions. These small HII regions are thought
to be at their earliest evolutionary phase and associated with the youngest
massive stars. The observations suggest that these HII regions are
characterized by high densities, supersonic flows and steep density gradients,
consistent with accretion and outflows that would be associated with the
formation of massive stars.Comment: ApJ in pres
L'Espermatogènesi en els crancs (Crustacea, Brachyura) : un model atípic de condensació del nucli espermàtic
Els espermatozoides dels crustacis decàpodes es caracteritzen per tenir un nucli amb
cromatina poc condensada, un acrosoma complex i un citoplasma reduït sense flagel. Es
disposa d'una àmplia informació sobre la ultraestructura i variabilitat morfològica dels espermatozoides
dels crustacis decàpodes, i particularment dels braquiürs, ja que la seva especificitat
ha permès utilitzar-los com a caràcter filogenètic, però el procés d'espermatogènesi
i la naturalesa de les proteïnes associades a la cromatina dels espermatozoides són
qüestions encara no resoltes. En aquest treball hem tractat aquestes dues qüestions utilitzant
com a model dues espècies de braquiürs: la cabra de mar, Maja brachydactyla, i el bou
de mar, Cancer pagurus. D'aquesta manera, hem realitzat una breu descripció de la morfologia
de l'aparell reproductor masculí de M. brachydactyla, hem localitzat el lloc on es desenvolupa
l'espermatogènesi i hem descrit la formació dels espermatòfors que són transferits
a la femella. A continuació, hem comparat el procés d'espermatogènesi de M. brachydactyla,
amb els estudis fets en altres espècies, considerant de manera preferent la formació de
l'acrosoma. Finalment, hem descrit diferents aspectes del nucli dels espermatozoides dels
braquiürs, fent un estudi específic de les proteïnes associades al nucli de l'espermatozoide
de C. pagurus.Decapods crustacean spermatozoa are characterized by a nucleus containing a low condensed
chromatin, a complex acrosome and reduced cytoplasm lacking of flagellum. Large
information on ultrastructure and morphological variability of the spermatozoa is available
in crustacean particularly, in Brachyuran, since their specificity has been used as a phylogenetic
character. However, the spermatogenesis and the nature of the proteins associated
to chromatin in the nucleus of the spermatozoa are still unclear. In the present study,
we have dealt both topics using two brachyuran species as model: the spider crab, Maja
brachydactyla and the edible crab, Cancer pagurus. Thus, we have briefly described the morphology
of the male reproductive system of M. brachydactyla in order to locate the spermatogenesis
process and to describe the formation of the spermatophore transferred to the
female. Finally, we have also described and compared with previous studies, the spermatogenesis
process of M. brachydactyla with special attention to the acrosomal vesicle. We
have finished our study describing the different characters presented in the nucleus of the
spermatozoa, with special reference to the proteins associated to chromatin in C. pagurus
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