Magnetic field geometry of an unusual cometary cloud Gal 110-13

Abstract

Aims. We carried out optical polarimetry of an isolated cloud, Gal 110-13, to map the plane-of-the-sky magnetic field geometry. The main aim of the study is to understand the most plausible mechanism responsible for the unusual cometary shape of the cloud in the context of its magnetic field geometry. Methods. When unpolarized starlight passes through the intervening interstellar dust grains that are aligned with their short axes parallel to the local magnetic field, it gets linearly polarized. The plane-of-the-sky magnetic field component can therefore be traced by doing polarization measurements of background stars projected on clouds. Because the light in the optical wavelength range is most efficiently polarized by the dust grains typically found in the outer layers of the molecular clouds, optical polarimetry enables us to trace the magnetic field geometry of the outer layers of the clouds. Results. We made R-band polarization measurements of 207 stars in the direction of Gal 110-13. The distance of Gal 110-13 was determined as ∼450 ± 80 pc using our polarization and 2MASS near-infrared data. The foreground interstellar contribution was removed from the observed polarization values by observing a number of stars located in the vicinity of Gal 110-13 which has Hipparcos parallax measurements. The plane-of-the-sky magnetic field lines are found to be well ordered and aligned with the elongated structure of Gal 110-13. Using structure function analysis, we estimated the strength of the plane-of-the-sky component of the magnetic field as ∼25 μG. Conclusions. Based on our results and comparing them with those from simulations, we conclude that compression by the ionization fronts from 10 Lac is the most plausible cause of the comet-like morphology of Gal 110-13 and of the initiation of subsequent star formation.

Probing the magnetic fields in L1415 and L1389

“…But, in principle, to obtain the actual magnetic field morphology in a cloud, the foreground polarization contribution has to be excluded. From the previous polarization studies by us towards the clouds located at distances less than ∼500 pc (e.g., Soam et al, 2013;Neha et al, 2016) and from the literature (Li et al, 2009), it was found that the change occurred to the values of the θP after correcting for the foreground contribution is not noteworthy specially if the observed P is relatively higher (i.e. 1%).…”

“…The instrumental polarization of AIMPOL has been 4.5 ± 0.1 116 ± 1 † Values in R band from Schmidt et al (1992) ‡ Values in V band from Schmidt et al (1992) checked by observing un-polarized standards and found nearly invariable with a value of ∼ 0.1% by Soam et al (2013Soam et al ( , 2015 and Neha et al (2016). The polarized standard stars observed by us to calibrate our polarization values are summarized in Table 2.…”

On the observational behaviour of the highly polarized Type IIn supernova SN 2017hcc

“…The instrumental polarization of AIMPOL is generally found to be small, at ∼ 0.1 per cent (see, e.g. Medhi et al 2007;Pandey et al 2009;Das et al 2013;Eswaraiah et al 2012Eswaraiah et al , 2013Patel et al 2013;Soam et al 2015;Neha et al 2016;Rakshit et al 2017;Wang et al 2017;Lee et al 2018, and references therein). This was verified by the observations of the unpolarized standard star HD 12021 (Schmidt, Elston & Lupie 1992).…”

Polarization of seven MBM clouds at high Galactic latitude

“…Thus, the stars, which are classified as main sequence stars, are plotted in an A V versus distance diagram to estimate the distance of the cloud. This method was used to estimate distances to a number of clouds (e.g., Maheswar et al, 2011;Soam et al, 2013;Eswaraiah et al, 2013;Neha et al, 2016). In Fig.…”