arXiv subjects

Arpan Ghosh

Publications and source records attributed to Arpan Ghosh.

28 records · Page 2Linked to original sources

arXiv2021

Gaia 20eae: A newly discovered episodically accreting young star

The Gaia Alert System issued an alert on 2020 August 28, on Gaia 20eae when its light curve showed a $\sim$4.25 magnitude outburst. We present multi-wavelength photometric and spectroscopic follow-up observations of this source since 2020 August and identify it as the newest member of the FUor/EXor family of sources. We find that the present brightening of Gaia 20eae is not due to the dust clearing event but due to an intrinsic change in the spectral energy distribution. The light curve of Gaia 20eae shows a transition stage during which most of its brightness ($\sim$3.4 mag) has occurred at a short timescale of 34 days with a rise-rate of 3 mag/month. Gaia 20eae has now started to decay at a rate of 0.3 mag/month. We have detected a strong P Cygni profile in H$α$ which indicates the presence of winds originating from regions close to the accretion. We find signatures of very strong and turbulent outflow and accretion in Gaia 20eae during this outburst phase. We have also detected a red-shifted absorption component in all the Ca II IR triplet lines consistent with signature of hot in-falling gas in the magnetospheric accretion funnel. This enables us to constrain the viewing angle with respect to the accretion funnel. Our investigation of Gaia 20eae points towards magnetospheric accretion being the phenomenon for the current outburst.

astro-ph.SR↗

arXiv2021

Sh 2-301: a blistered H II region undergoing star formation

We present a multiwavelength study of the H II region Sh 2-301 (S301) using deep optical data, near-infrared data, radio continuum data and other archival data at longer wavelengths. A cluster of young stellar objects (YSOs) is identified in the north-east (NE) direction of S301. The Hα and radio continuum images trace the distribution of the ionized gas surrounding a massive star ALS 207, and the S301 H II region is bounded by an arc-like structure of gas and dust emission in the south-eastern direction. The north-western part of S301 seems to be devoid of gas and dust emission, while the presence of molecular material between the NE cluster and the central massive star ALS 207 is found. The distribution of warm dust emission, ionized gas, and neutral hydrogen together suggests a blistered morphology of the S301 H II region powered by ALS 207, which appears to be located near the edge of the cloud. The location of the NE cluster embedded in the cold molecular cloud is found opposite to the blistered morphology. There is a noticeable age difference investigated between the massive star and the NE cluster. This age difference, pressure calculation, photodissociation regions (PDRs), and the distribution of YSOs favour the positive feedback of the massive star ALS 207 in S301. On a wider scale of S301, the H II region and the young stellar cluster are depicted toward the central region of a hub-filamentary system, which is evident in the infrared images.

astro-ph.GA↗

arXiv2020

PAH and nbL Features Detection in Planetary Nebulae NGC 7027 and BD +303639 with TIRCAM2 Instrument on 3.6m DOT

High resolution infrared imaging observations of the young Planetary Nebulae NGC 7027 and BD +303639, taken with the newly installed TIFR Infrared Camera-II (TIRCAM2) on 3.6m Devasthal Optical Telescope (DOT), ARIES, Nainital, are being reported. The images are acquired in J, H, K, polycyclic aromatic hydrocarbon (PAH) and narrow-band L (nbL) filters. The observations show emission from warm dust and PAHs in the circumstellar shells. The imaging of the two objects are among the first observations in PAH and nbL bands using TIRCAM2 on DOT. The NGC 7027 images in all bands show similar elliptical morphology with ~6".7 and ~4".5 semi-major and semi-minor axes. Considering size up to 10% of peak value the nebula extends upto 8" from the central star revealing a multipolar evolution. The relatively cooler BD +303639 shows a rectangular-ring shaped nebula. In J and H bands it shows an angular diameter of ~8", while a smaller ~6".9 size is observed in K, PAH and nbL bands. The 3.28 micron emission indicates presence of PAHs at about 6000 and 5000 AU from the central stars in NGC 7027 and BD +303639 respectively. Analysis suggests domination of neutral PAHs in BD+303639, while in NGC 7027 there is higher ionization and more processed PAH population.

astro-ph.SR↗

arXiv2020

The disintegrating old open cluster Czernik 3

We have performed a detailed analysis of the Czernik 3 (Cz3) open cluster by using deep near-infrared photometry taken with TIRCAM2 on 3.6m Devasthal optical telescope along with the recently available high quality proper motion data from the {\it Gaia} DR2 and deep photometric data from Pan-STARRS1. The cluster has a highly elongated morphology with fractal distribution of stars. The core and cluster radii of the cluster are estimated as 0.5 pc and 1.2 pc, respectively. We have identified 45 stars as cluster members using the {\it Gaia} proper motion data. The distance and age of the cluster are found to be $3.5\pm0.9$ kpc and $0.9^{+0.3}_{-0.1}$ Gyr, respectively. The slope of the mass function $`Γ'$ in the cluster region, in the mass range $\sim$0.95$<$M/M$_\odot$$<$2.2, is found to be $-1.01\pm0.43$. The cluster shows the signatures of mass-segregation and is dynamically relaxed (dynamical age=10 Myr). This along with its small size, big tidal radius, low density/large separation of stars, and elongated and distorted morphology, indicate that the Cz3 is a loosely bound disintegrating cluster under the influence of external tidal interactions.

astro-ph.GA↗

arXiv2020

Stellar cores in the Sh 2-305 H II region

Using our deep optical and near-infrared photometry along with multiwavelength archival data, we here present a detailed study of the Galactic H II region Sh 2-305, to understand the star/star-cluster formation. On the basis of excess infra-red emission, we have identified 116 young stellar objects (YSOs) within a field of view of ~ 18.5 arcminute x 18.5 arcminute, around Sh 2-305. The average age, mass and extinction (A_V) for this sample of YSOs are 1.8 Myr, 2.9 solar mass and 7.1 mag, respectively. The density distribution of stellar sources along with minimal spanning tree calculations on the location of YSOs reveals at least three stellar sub-clusterings in Sh 2-305. One cluster is seen toward the center (i.e., Mayer 3), while the other two are distributed toward the north and south directions. Two massive O-type stars (VM2 and VM4; ages ~ 5 Myr) are located at the center of the Sh 2-305 H II region. The analysis of the infrared and radio maps traces the photon dominant regions (PDRs) in the Sh 2-305. Association of younger generation of stars with the PDRs is also investigated in the Sh 2-305. This result suggests that these two massive stars might have influenced the star formation history in the Sh 2-305. This argument is also supported with the calculation of various pressures driven by massive stars, slope of mass function/K-band luminosity function, star formation efficiency, fraction of Class I sources, and mass of the dense gas toward the sub-clusterings in the Sh 2-305.

astro-ph.SR↗

arXiv2019

Modified Reynolds equation for steady flow through a curved pipe

A modified Reynolds equation governing the steady flow of a fluid with low Reynolds number through a curvilinear, narrow tube, with its derivation from Stokes equations through asymptotic methods is presented. The channel considered may have large curvature and torsion. Approximations of the velocity and the pressure of the fluid inside the channel are constructed by artificially imposing appropriate boundary conditions at the inlet and the outlet. A justification for the approximations is provided along with a comparison with a simpler case.

math-ph↗

arXiv2018

TIFR Near Infrared Imaging Camera-II on the 3.6-m Devasthal Optical Telescope

TIFR Near Infrared Imaging Camera-II is a closed-cycle Helium cryo-cooled imaging camera equipped with a Raytheon 512 x 512 pixels InSb Aladdin III Quadrant focal plane array having sensitivity to photons in the 1-5 microns wavelength band. In this paper, we present the performance of the camera on the newly installed 3.6-m Devasthal Optical Telescope (DOT) based on the calibration observations carried out during 2017 May 11-14 and 2017 October 7-31. After the preliminary characterization, the camera has been released to the Indian and Belgian astronomical community for science observations since 2017 May. The camera offers a field-of-view of ~86.5 arcsec x 86.5 arcsec on the DOT with a pixel scale of 0.169 arcsec. The seeing at the telescope site in the near-infrared bands is typically sub-arcsecond with the best seeing of ~0.45 arcsec realized in the near-infrared K-band on 2017 October 16. The camera is found to be capable of deep observations in the J, H and K bands comparable to other 4-m class telescopes available world-wide. Another highlight of this camera is the observational capability for sources up to Wide-field Infrared Survey Explorer (WISE) W1-band (3.4 microns) magnitudes of 9.2 in the narrow L-band (nbL; lambda_{cen} ~3.59 microns). Hence, the camera could be a good complementary instrument to observe the bright nbL-band sources that are saturated in the Spitzer-Infrared Array Camera ([3.6] <= 7.92 mag) and the WISE W1-band ([3.4] <= 8.1 mag). Sources with strong polycyclic aromatic hydrocarbon (PAH) emission at 3.3 microns are also detected. Details of the observations and estimated parameters are presented in this paper.

astro-ph.IM↗

arXiv2017

A two dimensional model of curvilinear blood vessels with layered elastic walls

We present a two dimensional model describing the elastic behaviour of the wall of a curved blood vessel. The wall has a laminate structure consisting of several anisotropic layers of varying thickness and is assumed to be much smaller in thickness than the radius of the vessel which itself is allowed to vary. Our two-dimensional model takes the interaction of the wall with the surrounding tissue and the blood flow into account and is obtained via a dimension reduction procedure. The curvature and twist of the vessel axis as well as the anisotropy of the laminate wall present the main challenges in applying the dimension reduction procedure so plenty of examples of canonical shapes of vessels and their walls are supplied with explicit systems of differential equations at the end.

q-bio.TO↗

arXiv2016

On sub-Riemannian geodesics in $SE(3)$ whose spatial projections do not have cusps

We consider the problem $\mathbf{P_{curve}}$ of minimizing $\int \limits_0^L \sqrt{ξ^2 + κ^2(s)} \, {\rm d}s$ for a curve $\mathbf{x}$ on $\mathbb R$ with fixed boundary points and directions. Here the total length $L\geq 0$ is free, $s$ denotes the arclength parameter, $κ$ denotes the absolute curvature of $\mathbf{x}$, and $ξ>0$ is constant. We lift problem $\mathbf{P_{curve}}$ on $\mathbb R^3$ to a sub-Riemannian problem $\mathbf{P_{mec}}$ on $\operatorname{SE(3)}\nolimits/(\{\mathbf{0}\}\times \operatorname{SO(2)}\nolimits)$. Here, for admissible boundary conditions, the spatial projections of sub-Riemannian geodesics do not exhibit cusps and they solve problem $\mathbf{P_{curve}}$. We apply the Pontryagin Maximum Principle (PMP) and prove Liouville integrability of the Hamiltonian system. We derive explicit analytic formulas for such sub-Riemannian geodesics, relying on the co-adjoint orbit structure, an underlying Cartan connection, and the matrix representation of $\operatorname{SE(3)}\nolimits$ arising in the Cartan-matrix. These formulas allow us to extract geometrical properties of the sub-Riemannian geodesics with cuspless projection, such as planarity conditions, explicit bounds on their torsion, and their symmetries. Furthermore, they allow us to parameterize all admissible boundary conditions reachable by geodesics with cuspless spatial projection. Such projections lay in the upper half space. We prove this for most cases, and the rest is checked numerically. Finally, we employ the formulas to numerically solve the boundary value problem, and visualize the set of admissible boundary conditions.

math.OC↗

arXiv2011

Diffusion, Convection and Erosion on SE(3)/({0} \times SO(2)) and their Application to the Enhancement of Crossing Fibers

In this article we study both left-invariant (convection-)diffusions and left-invariant Hamilton-Jacobi equations on the space SE(3)/({0} \times SO(2)) of 3D-positions and orientations naturally embedded in the group SE(3) of 3D-rigid body movements. The general motivation for these (convection-)diffusions and erosions is to obtain crossing-preserving fiber enhancement on probability densities defined on the space of positions and orientations. The linear left-invariant (convection-)diffusions are forward Kolmogorov equations of Brownian motions on SE(3)/({0}\timesSO(2)) and can be solved by convolution with the corresponding Green's functions or by a finite difference scheme. The left-invariant Hamilton-Jacobi equations are Bellman equations of cost processes on SE(3)/({0}\timesSO(2)) and they are solved by a morphological convolution with the corresponding Green's functions. Furthermore, we consider pseudo-linear scale spaces on the space of positions and orientations that combines dilation and diffusion in a single evolution. In our design and analysis for appropriate linear, non-linear, morphological and pseudo-linear scale spaces on SE(3)/({0}\timesSO(2)) we employ the underlying differential geometry on SE(3), where the frame of left-invariant vector fields serves as a moving frame of reference. Furthermore, we will present new and simpler finite difference schemes for our diffusions, which are clear improvements of our previous finite difference schemes. We apply our theory to the enhancement of fibres in magnetic resonance imaging (MRI) techniques for imaging water diffusion processes in brain white matter. We provide experiments of our crossing-preserving evolutions on neural images of a human brain containing crossing fibers.

math.AP↗