In addition to the well-known 11-year solar cycle, the Sun's magnetic activity also shows significant variation on shorter time scales, e.g. between one and two years. We observe a quasi-biennial ...(2-year) signal in the solar p-mode oscillation frequencies, which are sensitive probes of the solar interior. The signal is visible in Sun-as-a-star data observed by different instruments and here we describe the results obtained using BiSON, GOLF, and VIRGO data. Our results imply that the 2-year signal is susceptible to the influence of the main 11-year solar cycle. However, the source of the signal appears to be separate from that of the 11-year cycle. We speculate as to whether it might be the signature of a second dynamo, located in the region of near-surface rotational shear.
It is well known that in the Sun, the frequencies and amplitudes of acoustic modes vary throughout the solar cycle. Indeed, while the magnetic activity goes towards its maximum, the frequencies of ...the modes increase and their amplitudes decrease. We have analyzed data from the CoRoT mission on a few stars that exhibit solar-like oscillations. The study of HD49933 (observed during 60 days and 137 days spanning a total of 400 days) showed a modulation of the maximum amplitude per radial mode and the frequency shifts of the modes, showing magnetic activity in this rapidly rotating star. Moreover, both properties vary in an anticorrelated way and the data allowed us to establish a lower limit for the activity-cycle period of 120 days. Measurements in Ca H and K lines confirmed that this star is in the "active stars" category. We will also discuss the results obtained for other targets such as HD181420 and HD49835 for which we have investigated a similar behavior.
The IRIS network has been operated continuously since July 1st 1989. To date, it has acquired more than a complete solar cycle of full-disk helioseismic data which has been used to constrain the ...structure and rotation of the deep solar interior. However, the duty cycle of the network data has never reached initial expectations. To improve this situation, several cooperations have been developed with teams collecting observations with similar instruments. This paper demonstrates that we are able to merge data from these different instruments in a consistent manner resulting in a very significant improvement in network duty cycle over more than one solar cycle initiating what we call the IRIS++ network.
With a possible angular resolution down to 0.1-0.2 millisecond of arc using the 330 m baselines and the access to the 600-900 nm spectral domain, the CHARA Array is ideally configured for focusing on ...precise and accurate fundamental parameters of stars. CHARA/SPICA (Stellar Parameters and Images with a Cophased Array) aims at performing a large survey of stars all over the Hertzsprung-Russell diagram. This survey will also study the effects of the different kinds of variability and surface structure on the reliability of the extracted fundamental parameters. New surface-brightness-colour relations will be extracted from this survey, for general purposes on distance determination and the characterization of faint stars. SPICA is made of a visible 6T fibered instrument and of a near-infrared fringe sensor. In this paper, we detail the science program and the main characteristics of SPICA-VIS. We present finally the initial performance obtained during the commissioning.
We have been monitoring the metal-poor Population II giant, HD 122563, for radial velocity variations since 2016 using the SONG telescope on Tenerife. We have detected the global seismic quantity, ...numax, which provides information related to the stellar parameters. By combining these data with complementary data, we derive a new precise surface gravity, radius and distance to the star. Our results are corroborated by using the parallax from Gaia DR2. We present these results and some of their implications.
We analyze Sun-as-a-star observations spanning over solar cycles 22 -- 24 from the ground-based network BiSON and solar cycles 23 -- 24 collected by the space-based VIRGO and GOLF instruments on ...board the {\it SoHO} satellite. Using simultaneous observations from all three instruments, our analysis suggests that the structural and magnetic changes responsible for modifying the frequencies remained comparable between cycle 23 and cycle 24 but differ from cycle 22. Thus we infer that the magnetic layer of the Sun has become thinner since the beginning of cycle 23 and continues during the current cycle.
The nearby metal-poor giant HD122563 is an important astrophysical laboratory for which to test stellar atmospheric and interior physics. It is also a benchmark star for which to calibrate methods to ...apply to large scale surveys. Recently it has been remeasured using various methodologies given the new high precision instruments at our disposal. However, inconsistencies in the observations and models have been found. In order to better characterise this star we have been measuring its radial velocities since 2016 using the Hertzsprung telescope (SONG network node). In this work we report the first detections of sun-like oscillations in this star, and to our knowledge, a detection in the most metal-poor giant to date. We apply the classical seismic scaling relation to derive a new surface gravity of \(\log g_{\nu} = 1.39 \pm 0.01\) dex. Constraints on the mass imposed by its PopII giant classification then yield a radius of \(30.8 \pm 1.0\) R\(_{\odot}\). By coupling this with recent interferometric measurements we infer a distance to the star of 306 \(\pm\) 9 pc. Data from the Gaia mission corroborates the distance hypothesis (\(d_{\rm GDR2}\) = 290 \(\pm\) 5 pc), and thus the updated fundamental parameters. We confirm the validity of the seismic scaling relation without corrections for surface gravity in metal-poor and evolved star regimes. The small discrepancy of 0.04 dex reduces to 0.02 dex by applying corrections to the scaling relations. The new constraints on the HR diagram (\(L_{\odot} = 381 \pm 26\)) reduce the disagreement between the stellar parameters and evolution models, however, a discrepancy still exists. Fine-tuned stellar evolution calculations show that this can be reconciled by changing the mixing-length parameter by an amount (--0.35) that is in agreement with predictions from recent 3D simulations and empirical results.
This paper describes a high-performance liquid chromatographic method (HPLC) with fluorometric detection for the analysis of granisetron in plasma. The detection is performed at 305 nm for excitation ...and 365 n, for emission. The method involves sample clean-up by liquid-liquid extraction. N-(1-Naphthyl) ethylenediamine dihydrochloride is used as internal standard. Toluene and phosphate buffer were added to 0.5 ml of plasma added to the internal standard. After extraction, the organic layer was separated and then evaporated to dryness. The residue was reconstituted in eluent mixture. An aliquot was injected onto the HPLC column, Spherisorb CN, equilibrated with an eluent mixture constituted by acetonitrile-phosphate buffer (pH 4.5) (15:85). The proposed technique is reproducible, selective, reliable, and sensitive. Linear detector responses were observed for the calibration curve standards in the range of 0.50 to 100 ng/ml. Extraction recovery from plasma proved to be more than 90%. Precision expressed as C.V. was in the range 2 to 8%. As low as 0.3 ng of granisetron per ml of plasma can be measured with good accuracy. The method has been validated, and stability testsunder various conditions have been performed. Its sensitivity is adequate for pharmacokinetic studies.
Continuum intensity images from PICARD/SODISM and SDO/HMI covering a 209 days period in 2011 are analyzed in order to extract mode parameters for spherical harmonics up to \(l=100\). SODISM ...helioseismology signal is affected by the low orbit of PICARD and by important gaps and CCD persistence effects. SODISM intensity signal has a lower signal to noise ratio and duty cycle than HMI and less modes were successfully fitted over the same period. A comparison of the rotation profiles obtained from both sets of continuum images shows however that the results remain compatible within one standard deviation of HMI formal errors.
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