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We present results from a study of starspot areas and temperatures primarily on active, ( f S ) ( T S ), single-lined spectroscopic binaries, determined using molecular absorption bands. Expanding upon our previous studies, we have analyzed multiorder echelle spectra of eight systems to simultaneously measure several di †erent molecular bands and chromospheric emission lines. We determined starspot parameters by Ðtting the molecular bands of interest, using spectra of inactive G and K stars as proxies for the nonspotted photosphere of the active stars, and using spectra of M stars as proxies for the spots. At least two bands with di †erent sensitivities are required. We found that Ðtting bands other than the TiO T eff 7055 and 8860 features does not greatly extend the temperature range or sensitivity of our technique.A The 8860 band is particularly important because of its sharply di †erent temperature sensitivity. We A did not Ðnd any substantial departures from or that we have measured previously based on singlef S T S order spectra. We reÐned our derived spot parameters using contemporaneous photometry where available. We found that using M giants as spot proxies for subgiant active stars often underestimates f S needed to Ðt the photometry ; this is presumably due to the increase in strength of the TiO bands with decreasing gravity. We also investigated correlations between and chromospheric emission, and we f S developed a simple method to measure nonspot temperature solely from our echelle spectra.

Abstract. We present the results of an extensive observing campaign on the O7.5 III star ξ Persei. The UV observations were obtained with the International Ultraviolet Explorer. ξ Per was monitored continuously in October 1994 during 10 days at ultraviolet and visual wavelengths. The ground-based optical observations include magnetic field measurements, Hα and He i λ6678 spectra, and were partially covered by photometry and polarimetry. We describe a method to automatically remove the variable contamination of telluric lines in the groundbased spectra. The aim of this campaign was to search for the origin of the cyclical wind variability in this star. We determined a very accurate period of 2.086(2) d in the resonance lines of Si iv and in the subordinate N iv and Hα line profiles. The epochs of maximum absorption in the UV resonance lines due to discrete absorption components (DACs) coincide in phase with the maxima in blue-shifted Hα absorption. This implies that the periodic variability originates close to the stellar surface. The phase−velocity relation shows a maximum at −1400 km s −1 . The general trend of these observations can be well explained by the corotating interaction region (CIR) model. In this model the wind is perturbed by one or more fixed patches on the stellar surface, which are most probably due to small magnetic field structures. Our magnetic field measurements gave, however, only a null-detection with a 1σ errorbar of 70 G in the longitudinal component. Some observations are more difficult to fit into this picture. The 2-day period is not detected in the photospheric/transition region line He i λ6678. The dynamic spectrum of this line shows a pattern indicating the presence of non-radial pulsation, consistent with the previously reported period of 3.5 h. The edge variability around −2300 km s −1 in the saturated wind lines of C iv and N v is nearly identical to the edge variability in the unsaturated Si iv line, supporting the view that this type of variability is also due to the moving DACs. A detailed analysis using Fourier reconstructions reveals that each DAC actually consists of 2 different components: a "fast" and a "slow" one which merge at higher velocities.

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The literature on the λ Boo stars has grown to become somewhat heterogenous, as different authors have applied different criteria across the UV, optical and infrared regions to determine the membership status of λ Boo candidates. We aim to clear up the confusion by consulting the literature on 212 objects that have been considered as λ Boo candidates, and subsequently evaluating the evidence in favour of their admission to the λ Boo class. We obtained new spectra of ∼90 of these candidates and classified them on the MK system to aid in the membership evaluations. The re-evaluation of the 212 objects resulted in 64 members and 103 non-members of the λ Boo class, with a further 45 stars for which membership status is unclear. We suggest observations for each of the stars in the latter category that will allow them to be confidently included or rejected from the class. Our reclassification facilitates homogenous analysis on group members, and represents the largest collection of confirmed λ Boo stars known. c 0000 RAS

The λ Boo stars are a class of chemically peculiar Population I A-type stars characterized by under-abundances of the refractory elements, but near-solar abundances of carbon, nitrogen, oxygen, and sulfur. There is some evidence that λ Boo stars have higher frequencies of “bright” debris disks than normal A-type stars. The discovery of four exoplanets orbiting HR 8799, a λ Boo star with a resolved debris disk, suggests that the λ Boo phenomenon may be related to the presence of a dynamic debris disk, perhaps perturbed by migrating planets. However, only 64 λ Boo stars are known, and those stars were discovered with different techniques, making it problematic to use that sample for statistical purposes, including determining the frequency of debris disks. The purpose of this paper is to derive a new sample of λ Boo stars using a technique that does not lead to biases with respect to the presence of infrared excesses. Through spectroscopic observations in the southern hemisphere, we have discovered 33 λ Boo stars and have confirmed 12 others. As a step toward determining the proportion of λ Boo stars with infrared excesses, we have used WISE data to examine the infrared properties of this sample out to 22 μm. On this basis, we cannot conclude that λ Boo stars have a greater tendency than normal A-type stars to show infrared excesses. However, observing this sample at longer wavelengths may change that conclusion, as many λ Boo debris disks are cool and do not radiate strongly at 22 μm.

We present a detailed analysis of GRB 151006A, the first GRB detected by Astrosat CZT Im-ager (CZTI). We study the long term spectral evolution by exploiting the capabilities of Fermi and Swift satellites at different phases, which is complemented by the polarization measurement with the CZTI. While the light curve of the GRB in different energy bands show a simple pulse profile, the spectrum shows an unusual evolution. The first phase exhibits a hard-to-soft (HTS) evolution until ∼ 16 − 20 s, followed by a sudden increase in the spectral peak reaching a few MeV. Such a dramatic change in the spectral evolution in case of a single pulse burst is reported for the first time. This is captured by all models we used namely, Band function, Blackbody+Band and two blackbodies+power law. Interestingly, the Fermi Large Area Telescope (LAT) also detects its first photon (> 100 MeV) during this time. This new injection of energy may be associated with either the beginning of afterglow phase, or a second hard pulse of the prompt emission itself which, however, is not seen in the otherwise smooth pulse profile. By constructing Bayesian blocks and studying the hardness evolution we find a good evidence for a second hard pulse. The Swift data at late epochs (> T 90 of the GRB) also shows a significant spectral evolution consistent with the early second phase. The CZTI data (100-350 keV), though having low significance (1σ), show high values of polarization in the two epochs (77% to 94%), in agreement with our interpretation.