Seismology and activity of the F type star HD 49933

A 10-night asteroseismic observation programme has been conducted in January 2004 with the spectrometer Harps at the ES0 3.6-m telescope. The selected target, the 6th magnitude F5V star HD 49933, was chosen among the prime candidates of Corot, the European space mission dedicated to characterize stellar oscillations mode with high precision photometry measurements. This star shows important line profiles variations, indicating a surprisingly high activity with respect to its low rotation rate. However, with the help of tools developed for disentangling the signatures of activity and oscillations, we are able to observe its oscillation spectrum in the frequency range [1.2, 2.2 mHz]. We measure the large separation (88.7+-0.4 microHz) and the maximum amplitude (around 0.4+-0.1 m/s rms), respectively in agreement and marginal agreement with the predicted values.Comment: accepted in A&A Letter

How accurately can we age-date solar-type dwarfs using activity/rotation diagnostics?

It is well established that activity and rotation diminishes during the life of sun-like main sequence (~F7-K2V) stars. Indeed, the evolution of rotation and activity among these stars appears to be so deterministic that their rotation/activity diagnostics are often utilized as estimators of stellar age. A primary motivation for the recent interest in improving the ages of solar-type field dwarfs is in understanding the evolution of debris disks and planetary systems. Reliable isochronal age-dating for field, solar-type main sequence stars is very difficult given the observational uncertainties and multi-Gyr timescales for significant structural evolution. Observationally, significant databases of activity/rotation diagnostics exist for field solar-type field dwarfs (mainly from chromospheric and X-ray activity surveys). But how well can we empirically age-date solar-type field stars using activity/rotation diagnostics? Here I summarize some recent results for F7-K2 dwarfs from an analysis by Mamajek & Hillenbrand (2008), including an improved "gyrochronology" [Period(color, age)] calibration, improved chromospheric (R'_HK and X-ray (log Lx/Lbol) activity vs. rotation (via Rossby number) relations, and a chromospheric vs. X-ray activity relation that spans four orders of magnitude in log Lx/Lbol. Combining these relations, one can produce predicted chromospheric and X-ray activity isochrones as a function of color and age for solar type dwarfs.Comment: 8 pgs, to appear in proc. of 258th IAU Symposium "The Ages of Stars", eds. E.E. Mamajek, D.R. Soderblom, & R.F.G. Wyse (in press

Clinical, paraclinical and serological findings in Susac syndrome: an international multicenter study

Background: Susac syndrome (SuS) is a rare disorder thought to be caused by autoimmune-mediated occlusions of microvessels in the brain, retina and inner ear leading to central nervous system (CNS) dysfunction, visual disturbances due to branch retinal artery occlusions (BRAO), and hearing deficits. Recently, a role for anti-endothelial cell antibodies (AECA) in SuS has been proposed. Objectives: To report the clinical and paraclinical findings in the largest single series of patients so far and to investigate the frequency, titers, and clinical relevance of AECA in SuS. Patients and methods: A total of 107 serum samples from 20 patients with definite SuS, 5 with abortive forms of SuS (all with BRAO), and 70 controls were tested for AECA by immunohistochemistry employing primate brain tissue sections. Results: IgG-AECA >1:100 were detected in 25% (5/20) of patients with definite SuS and in 4.3% (3/70) of the controls. Median titers were significantly higher in SuS (1:3200, range 1:100 to 1:17500) than in controls (1:100, range 1:10 to 1:320); IgG-AECA titers >1:320 were exclusively present in patients with SuS; three controls had very low titers (1:10). Follow-up samples (n = 4) from a seropositive SuS patient obtained over a period of 29 months remained positive at high titers. In all seropositive cases, AECA belonged to the complement-activating IgG1 subclass. All but one of the IgG-AECA-positive samples were positive also for IgA-AECA and 45% for IgM-AECA. SuS took a severe and relapsing course in most patients and was associated with bilateral visual and hearing impairment, a broad panel of neurological and neuropsychological symptoms, and brain atrophy in the majority of cases. Seropositive and seronegative patients did not differ with regard to any of the clinical or paraclinical parameters analyzed. Conclusions: SuS took a severe and protracted course in the present cohort, resulting in significant impairment. Our finding of high-titer IgG1 and IgM AECA in some patients suggest that humoral autoimmunity targeting the microvasculature may play a role in the pathogenesis of SuS, at least in a subset of patients. Further studies are warranted to define the exact target structures of AECA in SuS

A multi-site campaign to measure solar-like oscillations in Procyon. II. Mode frequencies

We have analyzed data from a multi-site campaign to observe oscillations in the F5 star Procyon. The data consist of high-precision velocities that we obtained over more than three weeks with eleven telescopes. A new method for adjusting the data weights allows us to suppress the sidelobes in the power spectrum. Stacking the power spectrum in a so-called echelle diagram reveals two clear ridges that we identify with even and odd values of the angular degree (l=0 and 2, and l=1 and 3, respectively). We interpret a strong, narrow peak at 446 muHz that lies close to the l=1 ridge as a mode with mixed character. We show that the frequencies of the ridge centroids and their separations are useful diagnostics for asteroseismology. In particular, variations in the large separation appear to indicate a glitch in the sound-speed profile at an acoustic depth of about 1000 s. We list frequencies for 55 modes extracted from the data spanning 20 radial orders, a range comparable to the best solar data, which will provide valuable constraints for theoretical models. A preliminary comparison with published models shows that the offset between observed and calculated frequencies for the radial modes is very different for Procyon than for the Sun and other cool stars. We find the mean lifetime of the modes in Procyon to be 1.29 +0.55/-0.49 days, which is significantly shorter than the 2-4 days seen in the Sun.Comment: accepted for publication in Ap

HAYDN: High-precision AsteroseismologY of DeNse stellar fields

In the last decade, the Kepler and CoRoT space-photometry missions have demonstrated the potential of asteroseismology as a novel, versatile and powerful tool to perform exquisite tests of stellar physics, and to enable precise and accurate characterisations of stellar properties, with impact on both exoplanetary and Galactic astrophysics. Based on our improved understanding of the strengths and limitations of such a tool, we argue for a new small/medium space mission dedicated to gathering high-precision, high-cadence, long photometric series in dense stellar fields. Such a mission will lead to breakthroughs in stellar astrophysics, especially in the metal poor regime, will elucidate the evolution and formation of open and globular clusters, and aid our understanding of the assembly history and chemodynamics of the Milky Way’s bulge and a few nearby dwarf galaxies

Optical Coherence Tomography (OCT) in Neurologic Disease

Optical coherence tomography (OCT) has evolved dramatically since the first reports of this technology in 1991, and has become an integral part of the ophthalmology evaluation.curriculum_fellow; VBnflaopticalcoherencetomography; KBDpapilledema; KBDopticneuritismultiplesclerosis, KBDraisedintracranialpressur

Neuro-Ophthalmology and Lymphocytic Hypophysitis

Lymphocytic hypophysitis is a rare inflammatory disorder affecting the sellar region. LH typically presents in the third trimester of pregnancy, although nulliparous and male patients have been reported. Two cases of LH with neuroophthalmologic symptoms will be presented

Optical Coherence Tomography (OCT) in Neurologic Disease

Optical coherence tomography (OCT) has evolved dramatically since the first reports of this technology in 1991, and has become an integral part of the ophthalmology evaluation.curriculum_fellow; KBDpapilledema; KBDopticneuritismultiplesclerosis; VBnflaopticalcoherencetomography; GVSoctandms, KBDraisedintracranialpressur

Autoimmune Encephalitis: GFAP, DPPX, Other

Paraneoplastic (classic) encephalitis syndromes are commonly associated with, but often present before the diagnosis of, an underlying neoplasm, most commonly small cell lung cancer (SCLC), lymphoma, thymoma or various other neoplasms. These are T-cell medicated diseases that rapidly produce neuronal dysfunction that is usually irreversible; the syndromic antibody is typically not pathogenic. In contrast, the more recently described autoimmune encephalitis syndromes are associated with pathogenic antibodies that target cell surface or synapse proteins, are less commonly associated with an underlying neoplasm, and are much more treatment-responsive than the "paraneoplastic" category. The rate of these autoimmune encephalitidies appears to be increasing over time.SMm

Autoimmune Encephalitis: GFAP, DPPX, Other New Autoimmune Syndromes

Paraneoplastic (classic) encephalitis syndromes are commonly associated with, but often present before the diagnosis of, an underlying neoplasm, most commonly small cell lung cancer (SCLC), lymphoma, thymoma or various other neoplasms. These are T-cell medicated diseases that rapidly produce neuronal dysfunction that is usually irreversible; the syndromic antibody is typically not pathogenic. In contrast, the more recently described autoimmune encephalitis syndromes are associated with pathogenic antibodies that target cell surface or synapse proteins, are less commonly associated with an underlying neoplasm, and are much more treatment-responsive than the "paraneoplastic" category. The rate of these autoimmune encephalitidies appears to be increasing over time.SMm