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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 used polarimetric standards are in fact variable or have polarization parameters that differ from their cataloged values. 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. For five years, 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. 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-size telescopes.

In this work, we study the magnetic field morphology of selected star-forming clouds spread over the galactic latitude ($b$) range, $-10^\circ$ to $10^\circ$. The polarimetric observation of clouds CB24, CB27 and CB188 are conducted to study the magnetic field geometry of those clouds from ARIES, Manora Peak, Nainital, India. These observations are combined with those of 14 further low latitude clouds available in the literature. Analyzing the polarimetric data of 17 clouds, we find that the alignment between the envelope magnetic field ($\theta_{B}^{env}$) and Galactic plane ($\theta_{GP}$) of the low-latitude clouds varies with their galactic longitudes ($l$). We observe a strong correlation between the longitude (\textit{l}) and the offset ($\theta_{off}=|\theta_B^{env}-\theta_{GP}|$) which shows that $\theta_{B}^{env}$ is parallel to the Galactic plane (GP) when the clouds are situated in the region, $115^\circ250^\circ$. To check the consistency of our results, the stellar polarization data available at Heiles (2000) catalogue are overlaid on DSS image of the clouds having mean polarization vector of field stars. The results are almost consistent with the Heiles data. The effect of turbulence of the cloud is also studied which may play an important role in causing the misalignment phenomenon observed between $\theta_{B}^{env}$ and $\theta_{GP}$. We have used \textit{Herschel} \textit{SPIRE} 500 $\mu m$ and \textit{SCUBA} 850 $\mu m$ dust continuum emission maps in our work to understand the density structure of the clouds., Comment: 22 pages, 7 figures. This is the Accepted Manuscript version of an article accepted for publication in Research in Astronomy and Astrophysics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. This Accepted Manuscript is published under a CC BY licence. The Version of Record is available soon online