18587770
High-Resolution Spectroscopy of the Yellow Hypergiant ρ Cassiopeiae from 1993 through the Outburst of 2000-2001
We present an overview of the spectral variability of the peculiar F-type hypergiant ρ Cas, obtained from our long-term monitoring campaigns over the past 8.5 yr with four spectrographs in the northern hemisphere. Between 2000 June and September an exceptional variability phase occurred when the V brightness dimmed by about a full magnitude. The star recovered from this deep minimum by 2001 April. It is the third outburst of ρ Cas on record in the last century. We observe TiO absorption bands in high-resolution near-IR spectra obtained with the Utrecht Echelle Spectrograph during the summer of 2000. TiO formation in the outer atmosphere occurred before the deep brightness minimum. Atmospheric models reveal that the effective temperature decreases by at least 3000 K, and the TiO shell is driven supersonically with 5.4 × 10-2 M☉ yr-1. Strong episodic mass loss and TiO have also been observed during the outbursts of 1945-1947 and 1985-1986. A detailed analysis of the exceptional outburst spectra is provided, by comparing with high-resolution optical spectra of the early M-type supergiants μ Cep (Ia) and Betelgeuse (Iab). During the outburst, central emission appears above the local continuum level in the split Na D lines. A prominent optical emission line spectrum appears in variability phases of fast wind expansion. The radial velocity curves of Hα and of photospheric metal absorption lines signal a very extended and velocity-stratified dynamic atmosphere. The outburst spectra indicate the formation of a low-temperature, optically thick circumstellar gas shell of 3 × 10-2 M☉ during 200 days, caused by dynamic instability of the upper atmosphere of this pulsating massive supergiant near the Eddington luminosity limit. We observe that the mass-loss rate during the outburst is of the same order of magnitude as has been proposed for the outbursts of η Carinae. We present calculations that correctly predict the outburst timescale, whereby the shell ejection is driven by the release of hydrogen ionization recombination energy.
7875116
The Millennium Outburst of the Cool Hypergiant Rho Cassiopeiae: Spectroscopy and Modeling
Between 2000 June and September an exceptional variability phase occurred in the peculiar F-type hypergiant Rho Cas, when the V-brightness dimmed by at least a full magnitude. The star recovered from this deep minimum by 2001 April. It is the third outburst of Rho Cas on record in the last century. We observe TiO absorption bands in high-resolution optical and near-IR spectra obtained with the Utrecht Echelle Spectrograph during the summer of 2000. TiO formation in the outer atmosphere occurred before the deep brightness minimum.Atmospheric models reveal that the effective temperature decreases by at least 3000 K, and the TiO shell is driven supersonically with Mdot =~5.4 10^-2 Msun/yr. Strong episodic mass loss and TiO have also been observed during the outbursts of 1945-47 and 1985-86. An analysis of the exceptional outburst spectra of 2000-01 is provided, by comparing with high-resolution optical spectra of the early M-type supergiants Mu Cep (Ia) and Betelgeuse (Iab). During the outburst, central emission appears above the local continuum level in the split Na D lines. The outburst spectra indicate the formation of a low- temperature, optically thick circumstellar gas shell of 3 10^-2 Msun during \~200 d, caused by dynamic instability of the upper atmosphere of this pulsating massive supergiant near the Eddington luminosity limit. We present an equation that correctly predicts the outburst time-scale, whereby the shell ejection is driven by the release of hydrogen recombination energy. We observe that the mass-loss rate during the outburst is of the same order of magnitude as has been proposed for the outbursts of Eta Carinae. The research results in this paper are described in further detail in Lobel et al. (2003). A spectral movie sequence of the outburst is available at this http URL
118228975
Mass loss rates in the Hertzsprung-Russell diagram
Discussion des donnees de la litterature concernant les pertes de masse de 271 etoiles de types O o M de population I, etablissement d'une relation M˙(T eff , L/L ○. ) representant la perte de masse-M˙ comme fonction de la temperature effective et de la luminosite et discussion de la precision de la procedure d'ajustement
15595029
Rapid variations of narrow absorption line components in the spectrum of P Cygni
Abstract We report the detection of rapid wavelength and intensity variations of narrow components in absorption line profiles of the hot galactic supergiant P Cygni . During most of the time, in 1 week of observations, there were two such components present. Although the period of observation is too short for firm conclusions, the velocity curves do not contradict the photometric period of 17.3 days. These curves may be interpreted as a double wave, ‘swinging in counterphase’. This observation would suggest the presence of one long wave over the stellar surface. The waves are possibly gravity waves with wavelengths of the order of half the stellar radius.
122476606
Design and performance of two CsI/NaI(T1) calorimeters in an internal target detector setup
Abstract The design, construction and performance of two total-absorption calorimeters for nuclear physics experiments is described. They are used in conjunction with an internal polarized deuterium target in the 2 GeV electron storage ring VEPP-3 in Novosibirsk to detect scattered electrons with energies up to 1.9 GeV and protons up to 600 MeV. Each calorimeter consists of three layers of CsI(T1) blocks followed by two layers of NaI(T1) blocks, a total of 16 radiation lengths of scintillating material. Scintillation light from the CsI(T1) is collected by wavelength-shifter plates and sensed by silicon photodiodes connected to charge-sensitive preamplifiers. The NaI(T1) is read out with photomultiplier tubes. An overview is given of the performance of these calorimeters together with the other components of the detector system under the background conditions of the internal target setup. The electron energy resolution obtained was ≈10% (FWHM).
122910362
Performance of a Polarized Deuterium Internal Target in a Medium-Energy Electron Storage Ring.
Abstract A polarized deuterium target internal to a medium-energy electron storage ring is described in the context of spin-dependent (e,e′d) and (e,e′p) experiments. Tensor polarized deuterium was produced in an atomic beam source and injected into a storage cell target. A Breit-Rabi polarimeter was used to monitor the injected atomic beam polarization. An electrostatic ion-extraction system and a Wien filter were utilized to measure on-line the atomic fraction of the target gas (71 ± 2%) in the storage cell. A target thickness t ⋍ 2 × 10 13 2 H/cm 2 was achieved. The target tensor polarization was varied from P zz + = 0.49(3) to P zz − = −0.89(6) while keeping the vector polarization P z at zero. The luminosity was ∼ 2 × 10 31 e − · 2 H · cm −2 s −1 at a beam current of 120 mA. The performance was stable over a fiv running period. A large acceptance non-magnetic detector system was used for the electron-proton (deuteron) coincidence measurement. It is demonstrated that these techniques result in low backgrounds due to scattering from species other than the polarized target gas and allow for fast and flexible orientation of the target spin. Specific issues such as interfacing the experiment to the storage ring and monitoring the performance of the target system are discussed in detail.
123437099
Elastic electron scattering from the multipole moment distributions of Mg 25
116061412
Spin observables in few-body systems: Results and prospects from Jefferson Lab
Selected highlights are presented of that part of the research program at Jefferson Lab, which is focused on properties of nucleons and few-body systems. The majority of the experiments described use a polarized beam in conjunction with a polarized target or an ejectile polarimeter. All depend heavily on the high quality of the beam produced by the CEBAF facility.