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We present the R -band polarimetry of two low-latitude Lynd's clouds L1495 and L1498 acquired with AIMPOL at Aryabhatta Research Institute of Observational Sciences, Nainital, India. The estimated polarization across the regions of L1495 and L1498 is typically in the range of ∼1–5 per cent and the position angle is typically in the range of ∼100°–137° from which we infer the morphologies of the corresponding magnetic field in the envelope region (⁠|$\theta_{\rm B}^{\rm env}$|⁠). In both clouds, the magnetic fields are found to be aligned with the galactic field (θGP). Due to their close proximity to the galactic plane, we incorporate the values of offset (⁠|$\theta _{\rm off} = |\theta _{\rm B}^{\rm env} - \theta _{\rm GP}|$|⁠) from this study into our previously established geometrical correlation between the variation in relative orientation with the galactic longitude. We find that the offsets estimated for two clouds L1495 and L1498 in this investigation are consistent with the offsets predicted by our previous study. We also generate the extinction map for the two clouds using the NICE technique, and the extinction structure is found to be analogous to the dust structure at the denser region of the cloud as obtained from the 500 µm dust continuum emission maps of Herschel 1 SPIRE. Three distinct cores with high extinction are detected in L1495, and two such cores are also detected in L1498. We also estimate the mean particle density (⁠|$\lt n_{\rm H_2}\gt $|⁠) at the peripheral region as well as the high extinction cores of the clouds. [ABSTRACT FROM AUTHOR]

Context. Optical polarimeters are typically calibrated using measurements of stars with known and stable polarization parameters. However, there is a lack of such stars available across the sky. Many of the currently available standards are not suitable for medium and large telescopes due to their high brightness. Moreover, as we find, some of the polarimetric standards used are in fact variable or have polarization parameters that differ from their cataloged values. Aims. Our goal is to establish a sample of stable standards suitable for calibrating linear optical polarimeters with an accuracy down to 10−3 in fractional polarization. Methods. For 4 yr, we have been running a monitoring campaign of a sample of standard candidates comprised of 107 stars distributed across the northern sky. We analyzed the variability of the linear polarization of these stars, taking into account the non-Gaussian nature of fractional polarization measurements. For a subsample of nine stars, we also performed multiband polarization measurements. Results. We created a new catalog of 65 stars (see Table 2) that are stable, have small uncertainties of measured polarimetric parameters, and can be used as calibrators of polarimeters at medium and large telescopes. [ABSTRACT FROM AUTHOR]

Aims. We intended to compile the most complete catalog of bona fide members and candidate members of the β Pictoris association, and to measure their rotation periods and basic properties from our own observations, public archives, and exploring the literature. Methods. We carried out a multi-observatories campaign to get our own photometric time series and collected all archived public photometric data time series for the stars in our catalog. Each time series was analyzed with the Lomb-Scargle and CLEAN periodograms to search for the stellar rotation periods. We complemented the measured rotational properties with detailed information on multiplicity, membership, and projected rotational velocity available in the literature and discussed star by star. Results. We measured the rotation periods of 112 out of 117 among bona fide members and candidate members of the β Pictoris association and, whenever possible, we also measured the luminosity, radius, and inclination of the stellar rotation axis. This represents to date the largest catalog of rotation periods of any young loose stellar association. Conclusions. We provided an extensive catalog of rotation periods together with other relevant basic properties useful to explore a number of open issues, such as the causes of spread of rotation periods among coeval stars, evolution of angular momentum, and lithium-rotation connection. [ABSTRACT FROM AUTHOR]

We report the results obtained from the optical polarimetric study of the light scattered by comets C/2013 V1 (Boattini) and 290P/Jager at lower phase angles. The polarimetric observations of two comets have been performed with the 1.04-m Sampurnanand telescope of Aryabhatta Research Institute of observational sciencES near Nainital in India on 2013 December4 and5, and on 2014 April 24 using R photometric band (λ = 630 Δλ, AX = 120 nm). We covered observations in both the pre- and post-perihelion passage of comets C/2013 V1 (Boattini) and 290P/Jager at two phase angles ~ 13° and 27°. The degree of polarization changes from (-1.4 ± 0.3) to (+2.8 ± 0.5)percent for comet C/2013 V1 (Boattini) and (-1.6 ± 0.5) to (+2.5 ± 0.5) per cent for comet 290P/Jager at phase angles ~13° and 27°, respectively. The change in the physical properties of cometary dust is being well studied from the polarization maps obtained for both the period of observations. It is found that the aperture polarization values are comparable to those of other comets. The variation in the brightness profile of both the comets from the standard canonical nature is also being observed in both the solar and antisolar direction during this phase which suggests the various physical evolutions influencing the cometary comae. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper is part of a multiwavelength study aimed at using complementary photometric, polarimetric and spectroscopic data to achieve an understanding of the activity process in late-type stars. Here, we present the study of FR Cnc, a young, active and spotted star. We performed analysis of All Sky Automated Survey 3 (ASAS-3) data for the years 2002-08 and amended the value of the rotational period to be 0.826518 d. The amplitude of photometric variations decreased abruptly in the year 2005, while the mean brightness remained the same, which was interpreted as a quick redistribution of spots. BVRC and IC broad-band photometric calibration was performed for 166 stars in FR Cnc vicinity. The photometry at Terskol Observatory shows two brightening episodes, one of which occurred at the same phase as the flare of 2006 November 23. Polarimetric BVR observations indicate the probable presence of a supplementary source of polarization. We monitored FR Cnc spectroscopically during the years 2004-08. We concluded that the radial velocity changes cannot be explained by the binary nature of FR Cnc. We determined the spectral type of FR Cnc as K7V. Calculated galactic space-velocity components ( U, V, W) indicate that FR Cnc belongs to the young disc population and might also belong to the IC 2391 moving group. Based on Li i λ6707.8 measurement, we estimated the age of FR Cnc to be between 10 and 120 Myr. Doppler tomography was applied to create a starspot image of FR Cnc. We optimized the goodness of fit to the deconvolved profiles for axial inclination, equivalent width and v sin i, finding v sin i= 46.2 km s −1 and i= 55°. We also generated a synthetic V-band light curve based on Doppler imaging that makes simultaneous use of spectroscopic and photometric data. This synthetic light curve displays the same morphology and amplitude as the observed one. The starspot distribution of FR Cnc is also of interest since it is one of the latest spectral types to have been imaged. No polar spot was detected on FR Cnc. [ABSTRACT FROM AUTHOR]

We have started a spectroscopic survey to identify new chromospherically active components and low-mass pre-main sequence (PMS) stars in recently discovered All Sky Automated Survey (ASAS) eclipsing binaries. In this paper, we briefly describe our scientific motivation, the observing tools and the results obtained from the first phase of this survey. Using the available observing facilities in India, the spectroscopic observations of a sample of 180 candidate eclipsing binary stars selected from ASAS-I&II releases were carried out during 2004–2006. The strength of Hα emission was used to characterize the level of chromospheric activity. Our spectroscopic survey reveals that out of 180 stars about 36 binary systems show excess Hα emission. One of the objects in our sample, ASAS 081700-4243.8, displays very strong Hα emission. Follow-up high-resolution spectroscopic observations reveal that this object is indeed very interesting and most likely a classical Be-type system with K0III companion. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper is part of a multiwavelength study aimed at using complementary photometric, polarimetric and spectroscopic data to achieve an understanding of the activity process in late-type stars. Here, we present the study of FR Cnc, a young, active and spotted star. We performed analysis of All Sky Automated Survey 3 (ASAS-3) data for the years 2002-08 and amended the value of the rotational period to be 0.826518 d. The amplitude of photometric variations decreased abruptly in the year 2005, while the mean brightness remained the same, which was interpreted as a quick redistribution of spots. BVRC and IC broad-band photometric calibration was performed for 166 stars in FR Cnc vicinity. The photometry at Terskol Observatory shows two brightening episodes, one of which occurred at the same phase as the flare of 2006 November 23. Polarimetric BVR observations indicate the probable presence of a supplementary source of polarization. We monitored FR Cnc spectroscopically during the years 2004-08. We concluded that the radial velocity changes cannot be explained by the binary nature of FR Cnc. We determined the spectral type of FR Cnc as K7V. Calculated galactic space-velocity components ( U, V, W) indicate that FR Cnc belongs to the young disc population and might also belong to the IC 2391 moving group. Based on Li i λ6707.8 measurement, we estimated the age of FR Cnc to be between 10 and 120 Myr. Doppler tomography was applied to create a starspot image of FR Cnc. We optimized the goodness of fit to the deconvolved profiles for axial inclination, equivalent width and v sin i, finding v sin i= 46.2 km s −1 and i= 55°. We also generated a synthetic V-band light curve based on Doppler imaging that makes simultaneous use of spectroscopic and photometric data. This synthetic light curve displays the same morphology and amplitude as the observed one. The starspot distribution of FR Cnc is also of interest since it is one of the latest spectral types to have been imaged. No polar spot was detected on FR Cnc. [ABSTRACT FROM AUTHOR]