arXiv subjects

Arijit Maiti

Publications and source records attributed to Arijit Maiti.

4 recordsLinked to original sources

arXiv2026

Exploring the long-term temporal variability in polarization through multi-epoch optical spectro-polarimetry - Part I: A sample of Herbig Ae/Be and classical Be stars

Polarization signatures across emission line features, together with their temporal evolution, offer a powerful probe of the circumstellar environments of astrophysical sources, on spatial scales otherwise inaccessible to direct imaging techniques. However, the photon-hungry nature of spectro-polarimetry has significantly limited the availability of such datasets in the literature. This work reports a multi-epoch spectro-polarimetric monitoring campaign targeting a sample of Herbig Ae/Be and classical Be stars. The initial observations were obtained during the commissioning and performance-verification phase of ProtoPol, a recently developed medium-resolution echelle spectro-polarimeter mounted on the Physical Research Laboratory (PRL) 2.5m telescope, Mt Abu, India. Given the limited number of comparable datasets available for this class of objects, follow-up observations of the same targets were carried out repeatedly over more than 28 months (December 2023-March 2026), enabling an investigation of the temporal behavior of their polarimetric properties. Our sample comprises 11 Herbig Ae/Be stars and 10 classical Be stars. Our observations found that, while the H$\alpha$ polarization remained relatively constant for the classical Be stars, they showed significant variability for most of the Herbig stars in the sample. The observations presented here constitute one of the rare multi-epoch spectro-polarimetric datasets spanning more than two years and should be of considerable interest to the broader astronomical community. This paper is Part-I of a two-part series of sample studies; corresponding results for symbiotic and red giant stars are presented in Part-II.

astro-ph.SR↗

arXiv2026

Discovery of variable polarization in H$\alpha$ profile of symbiotic star Y Gem: A case for orbital-phase dependent variation of Raman-scattered Ly$\beta$ emission

The geometry and morphology of symbiotic stars are conducive to exhibit a variety of scattering phenomena. The prominent among them is the Raman scattering of O VI doublet $\lambda \lambda$ 1032,1038 angstrom, which often show strongly polarized features in the visible spectrum. Similar Raman scattering of Ly$\beta$ photons has also been predicted to occur in symbiotic stars, though with fewer detections and with weak polarization amplitudes. Here, we present the discovery of strong variable polarization in the H$\alpha$ profile of a recently established symbiotic system Y Gem, over a period of nearly 22 months. This is, most likely, a very rare detection of the strongly polarized Raman scattered Ly$\beta$ photons, falling at the H$\alpha$ emission. Monte-Carlo simulations have been conducted to confirm the underlying Raman scattering process causing the polarized line profile, and a simple orbital model is constructed with typical parameters available in the recent literature along with a complementary low-resolution spectroscopic data. These simulations and models are then used to validate the observed polarization variation of H$\alpha$ at different orbital phases corresponding to the epochs of observations. The possibility of such strong variable H$\alpha$ polarization, being caused by Raman scattering of Ly$\beta$, would thus open up avenues of exploring such effects in various other astrophysical situations having similar morphology.

astro-ph.SR↗

arXiv2026

Development of ProtoPol: a medium resolution echelle spectro-polarimeter for PRL telescopes, Mt Abu, India -- Part I : the design, development and laboratory characterization

ProtoPol is a medium-resolution echelle spectro-polarimeter developed for Physical Research Laboratory (PRL) 1.2m and 2.5m telescopes, Mt. Abu, India. Though initially conceived to evaluate the development methodology of the echelle spectro-polarimeter, it was subsequently elevated to the level of a full-fledged back-end instrument for PRL telescopes. ProtoPol is developed on the traditional concept of using a half-wave plate with Wollaston prism to achieve the separation of two mutually orthogonal polarized beams. These separated beams are modulated and directed into an echelle spectrometer which is employs an echelle grating and two plane reflection gratings as the cross-dispersers. Therefore, the cross-dispersed spectra for two orthogonal polarized beams are recorded in multiple orders on a CCD detector. ProtoPol is designed to operate in the visible and near IR spectral range, 4000 - 9600 angstrom, with a spectral resolution ($\delta$$\lambda$) around 0.4-0.75 angstrom. The uniqueness of ProtoPol lies in its design which has entirely been developed with commercially available off-the-shelf optical and opto-mechanical components. This feature makes ProtoPol a noteworthy development as it offers a cost-effective way to develop spectro-polarimeters with such resolutions for small-aperture (2-3m) telescopes around the world, in a much shorter development period. ProtoPol has been successfully developed and commissioned on PRL 1.2m and 2.5m telescopes since December 2023, and a variety of observations have been carried out for instrument characterization, performance verification, and scientific purposes. This is the first of the two-part research articles series, wherein we present the design and development methodology of ProtoPol, along with its laboratory characterization and performance.

astro-ph.IM↗

arXiv2026

Development of ProtoPol: a medium resolution echelle spectro-polarimeter for PRL telescopes, Mt Abu, India -- Part II : the data-reduction pipeline, on-sky characterization $\&$ performance verification and first science results

We present the development of ProtoPol - a medium resolution echelle spectro-polarimeter for the PRL 1.2m and 2.5m telescopes at Mt Abu observatory, India. In this second and final part of the paper series, we report on the development of a dedicated data reduction pipeline of ProtoPol along with several characterization, performance evaluation, and scientific observations to quantify the performance of the instrument. ProtoPol provides a spectral resolution in the range of $\sim$0.4 - 0.75 angstrom across various orders in the visible wavelength range of 4000-9600 angstrom. On PRL 2.5m telescope, an SNR of 10 is achieved for $m_V\sim13.2$ source in 1 hour of integration time, and its throughput is estimated to be $\sim$6\% including all the contributing factors such as atmospheric transmission, telescope reflectivity, instrument's optics, CCD efficiency etc. ProtoPol achieved a linear polarization accuracy $\delta P \approx 0.1-0.2\%$ in 2 hours of integration time for a source with $m_V\approx8$. The instrumental polarization is determined to be around $0.1\%$. We also present the first science results with ProtoPol to demonstrate the capabilities of the instrument. A sample of Herbig Ae/Be stars, classical Herbig stars, Symbiotic stars, and AGB/post-AGB stars were observed over the period of one and half years for their spectro-polarimetry measurements covering various physical mechanisms such as intrinsic line polarization in Herbig and classical Be stars, Raman scattered features in Symbiotic stars, as well as continuum polarization in AGB/post-AGB stars to verify the polarization performance of the instrument.

astro-ph.IM↗