Broad Band Optical Polarimetric Study of IC 1805

We present the BVR broad band polarimetric observations of 51 stars belonging to the young open cluster IC 1805. Along with the photometric data from the literature we have modeled and subtracted the foreground dust contribution from the maximum polarization (P_{max}) and colour excess (E_{B-V}). The mean value of the P_max for intracluster medium and the foreground are found to be 5.008 +/-0.005 % and 4.865 +/-0.022 % respectively. Moreover, the mean value of the wavelength of maximum polarization (lambda_{max}) for intracluster medium is 0.541 +/- 0.003 micro m, which is quite similar as the general interstellar medium (ISM). The resulting intracluster dust component is found to have negligible polarization efficiency as compared to interstellar dust. Some of the observed stars in IC 1805 have shown the indication of intrinsic polarization in their measurements.Comment: 8 pages, 7 figures, Accepted for publication in MNRA

Is the β Pictoris member GJ 3039AB a physical binary? What the rotation periods tell us?

We have carried out a multi-band photometric monitoring of the close visual binary GJ 3039, consisting of a M4 primary and a fainter secondary component, and likely member of the young stellar association β Pictoris (24-Myr old). From our analysis we found that both components are photometric variables and, for the first time, we detected two micro-flare events. We measured from periodogram analysis of the photometric time series two rotation periods P = 3.355 d and P = 0.925 d, that we could attribute to the brighter GJ 3039A and the fainter GJ 3039B components, respectively. A comparison of these rotation periods with the period distribution of other β Pictoris members further supports that GJ 3039A is a member of this association. We find that also GJ 3039B could be a member, but the infrared magnitude differences between the two components taken from the literature and the photometric variability, which is found to be comparable in both stars, suggest that GJ 3039B could be a foreground star physically unbound to the primary A component

A Search for X-ray/UV Correlation in the Reflection-Dominated Seyfert 1 Galaxy Mrk 1044

Correlated variability between coronal X-rays and disc optical/UV photons provides a very useful diagnostic of the interplay between the different regions around an active galactic nucleus (AGN) and how they interact. AGN that reveal strong X-ray reflection in their spectra should normally exhibit optical/UV to X-ray correlation consistent with reprocessing -- where the optical/UV emission lag behind the X-rays. While such correlated delay has been seen in some sources, it has been absent in others. \rm{Mrk~1044} is one such source that has been known to reveal strong X-ray reflection in its spectra. In our analysis of three long \textit{XMM-Newton} and several \textit{Swift} observations of the source, we found no strong evidence for correlation between its UV and X-ray lightcurves both on short and long time scales. Among other plausible causes for the non-detection, we posit that higher X-ray variability than UV and strong general relativistic effects close to the black hole may also be responsible. We also present results from the spectral analysis based on \textit{XMM-Newton} and \textit{NuSTAR} observations, which show the strong soft X-ray excess and iron K$\alpha$ line in the 0.3--50 keV spectrum that can be described by relativistic reflection.Comment: Accepted for Publication in APJ, 13 pages, 11 figures, 2 table

Polarization in young open cluster NGC 6823

We present multiwavelength linear polarimetric observations of 104 stars towards the region of young open cluster NGC 6823. The polarization towards NGC 6823 is dominated by foreground dust grains and we found the evidence for the presence of several layers of dust towards the line of sight. The first layer of dust is located approximately within 200 pc towards the cluster, which is much closer to the Sun than the cluster (~ 2.1 kpc). The radial distribution of the position angles for the member stars are found to show a systematic change while the polarization found to reduce towards the outer parts of the cluster and the average position angle of coronal region of the cluster is very close to the inclination of the Galactic parallel (~ 32 degree). The size distribution of the grains within NGC 6823 is similar to those in general interstellar medium. The patchy distribution of foreground dust grains are suggested to be mainly responsible for the both differential reddening and polarization towards NGC 6823. The majority of the observed stars do not show the evidence of intrinsic polarization in their light.Comment: 16 pages, 6 tables, 11 figures, Accepted for publication in MNRA

Multi-wavelength polarimetric study towards the open cluster NGC 1893

We present multi-wavelength linear polarimetric observations for 44 stars of the NGC 1893 young open cluster region along with V-band polarimetric observations of stars of other four open clusters located between l ~160 to ~175 degree. We found evidence for the presence of two dust layers located at a distance of ~170 pc and ~360 pc. The dust layers produce a polarization Pv ~2.2%. It is evident from the clusters studied in the present work that, in the Galactic longitude range l ~160 to 175 degree and within the Galactic plane (|b| < 2 degree), the polarization angles remain almost constant, with a mean ~163 degree and a dispersion of 6 degree. The small dispersion in polarization angle could be due to the presence of uniform dust layer beyond 1 kpc. Present observations reveal that in case of NGC 1893, the foreground two dust layers, in addition to the intracluster medium, seems to be responsible for the polarization effects. It is also found that towards the direction of NGC 1893, the dust layer that exists between 2-3 kpc has a negligible contribution towards the total observed polarization. The weighted mean for percentage of polarization (Pmax) and the wavelength at maximum polarization ({\lambda}max) are found to be 2.59 \pm 0.02% and 0.55 \pm 0.01 \mum respectively. The estimated mean value of {\lambda}max indicates that the average size of the dust grains within the cluster is similar to that in the general interstellar medium. The spatial variation of the polarization is found to decrease towards the outer region of the cluster. In the present work, we support the notion, as already has been shown in previous studies, that polarimetry, in combination with (U-B)/(B-V) colour-colour diagram, is a useful tool for identifying non-members in a cluster.Comment: 36 pages, 12 figures, 10 tables, accepted for the publication in MNRA

LO Pegasi: An investigation of multi-band optical polarization

We present BVR polarimetric study of the cool active star LO Peg for the first time. LO Peg was found to be highly polarized among the cool active stars. Our observations yield average values of polarization in LO Peg: $P_B =0.387\pm 0.004$, $\theta_B = 88\deg\pm1\deg$; $P_V=0.351\pm0.004$, $\theta_V=91\deg\pm1\deg$; and $P_R= 0.335\pm0.003$, $\theta_R = 91\deg\pm1\deg$. Both the degree of polarization and the position angle are found to be variable. The semi-amplitude of the polarization variability in B, V and R bands are found to be $0.18\pm0.02$%, $0.13\pm0.01$% and $0.10\pm0.02$%, respectively. We suggest that the levels of polarization observed in LO Peg could be the result of scattering of an anisotropic stellar radiation field by an optically thin circumstellar envelope or scattering of the stellar radiation by prominence-like structures.Comment: 9 pages, 6 figures and 5 tables, Accepted for publication in MNRA