Broad-band optical polarimetric studies towards the Galactic young star cluster Berkeley 59

Eswaraiah, Chakali; Pandey, A. K.; Maheswar, G.; Chen, W. P.; Ojha, D. K.; Chandola, H. C.

doi:10.1111/j.1365-2966.2011.19908.x

Cited by 30 publications

(40 citation statements)

References 45 publications

(89 reference statements)

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“…Since AIMPOL is not equipped with a grid, care was taken to exclude stars with contaminations from the overlap of ordinary and extraordinary images of one star on the image of another star in the FOV. The data reduction and the procedures followed to measure the polarization of stars are similar to those described in Eswaraiah et al (2011Eswaraiah et al ( , 2012 • 34 16. 37 (in BVRI-bands on 13 December 2010) were observed using the 2-m telescope of the Inter University Center for Astronomy and Astrophysics (IUCAA) Girawali Observatory, India.…”

Section: Polarimetrymentioning

confidence: 99%

“…The instrumental polarization of AIMPOL on the 1.04-m ST has been monitored since 2004 for different projects and is 0.1% in different bands (e.g., Rautela et al 2004;Medhi et al 2007Medhi et al , 2008Medhi et al , 2010Eswaraiah et al 2011Eswaraiah et al , 2012. No correction for the instrumental polarization was applied to the data obtained with IFOSC since the instrumental polarization of the instrument on the 2-m telescope is <0.05 per cent.…”

Section: Polarimetrymentioning

confidence: 99%

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A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

Eswaraiah

Maheswar

Pandey

et al. 2013

A&A

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Aims. We aim to map the magnetic field geometry and to study the dust properties of the starless cloud, L1570, using multi-wavelength optical polarimetry and photometry of the stars projected on the cloud. Methods. The direction of the magnetic field component parallel to the plane of the sky of a cloud can be obtained using polarimetry of the stars projected on and located behind the cloud. It is believed that the unpolarized light from the stars background to the cloud undergoes selective extinction while passing through non-spherical dust grains that are aligned with their minor axes parallel to the cloud magnetic field. The emerging light becomes partially plane polarized. The observed polarization vectors trace the direction of the projected magnetic field of the cloud. We made R-band imaging polarimetry of the stars projected on a cloud, L1570, to trace the magnetic field orientation. We also made multi-wavelength polarimetric and photometric observations to constrain the properties of dust in L1570. Results. We estimated a distance of 394 ± 70 pc to the cloud using 2MASS JHK s colors. Using the values of the Serkowski parameters, σ 1 , , λ max , and the position of the stars on the near-infrared color-color diagram, we identified 13 stars that could possibly have intrinsic polarization and/or rotation in their polarization angles. One star, 2MASS J06075075+1934177, which is a B4Ve spectral type, shows diffuse interstellar bands in the spectrum in addition to the Hα line in emission. There is an indication for slightly bigger dust grains toward L1570 on the basis of the dust grain size-indicators such as λ max and R V values. The magnetic field lines are found to be parallel to the cloud structures seen in the 250 μm images (also in the 8 μm and 12 μm shadow images) of L1570. Based on the magnetic field geometry, the cloud structure, and the complex velocity structure, we conclude that L1570 is in the process of formation due to the converging flow material mediated by the magnetic field lines. A structure function analysis showed that in the L1570 cloud region the large-scale magnetic fields are stronger than the turbulent component of the magnetic fields. The estimated magnetic field strengths suggest that the L1570 cloud region is subcritical and hence could be strongly supported by the magnetic field lines.

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Section: Polarimetrymentioning

confidence: 99%

Section: Polarimetrymentioning

confidence: 99%

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

Eswaraiah

Maheswar

Pandey

et al. 2013

A&A

Self Cite

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“…The details of the observing facility and procedures used to estimate the polarization degree and polarization angles (P.A.) are described in Eswaraiah et al (2011Eswaraiah et al ( , 2012.…”

Section: Aimpol Polarimetrymentioning

confidence: 99%

“…Hence, polarized starlight is commonly used as a tracer of the B-field structure in the plane of sky (e.g., Chapman et al 2011;Clemens et al 2012a;Eswaraiah et al 2012). The first theory to explain dust alignment utilized a paramagnetic mechanism (DG alignment) (Davis & Greenstein 1951).…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength Stellar Polarimetry of the Filamentary Cloud IC5146. I. Dust Properties

Wang

Lai

Eswaraiah

et al. 2017

ApJ

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We present optical and near-infrared stellar polarization observations toward the dark filamentary clouds associated with IC5146. The data allow us to investigate the dust properties (this paper) and the magnetic field structure (Paper II). A total of 2022 background stars were detected in R c -, i ′ -, H-, and/or K-bands to A V 25 mag. The ratio of the polarization percentage at different wavelengths provides an estimate of λ max , the wavelength of peak polarization, which is an indicator of the small-size cutoff of the grain size distribution. The grain size distribution seems to significantly change at A V ∼ 3 mag, where both the average and dispersion of P Rc /P H decrease. In addition, we found λ max ∼ 0.6-0.9 µm for A V > 2.5 mag, which is larger than the ∼ 0.55 µm in the general ISM, suggesting that grain growth has already started in low A V regions. Our data also reveal that polarization efficiency (PE ≡ P λ /A V ) decreases with A V as a power-law in R c -, i ′ -, and K-bands with indices of -0.71±0.10, -1.23±0.10 and -0.53±0.09. However, H-band data show a power index change; the PE varies with A V steeply (index of -0.95±0.30) when A V < 2.88 ± 0.67 mag but softly (index of -0.25±0.06) for greater A V values. The soft decay of PE in high A V regions is consistent with the Radiative Aligned Torque model, suggesting that our data trace the magnetic field to A V ∼ 20 mag. Furthermore, the breakpoint found in H-band is similar to the A V where we found the P Rc /P H dispersion significantly decreased. Therefore, the flat PE-A V in high A V regions implies that the power index changes result from additional grain growth.

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“…To search for anomalies in the extinction law, we also constructed TCDs following the method proposed by Chini et al (1983Chini et al ( , 1990) and more recently used by Pandey et al (2000), Jose et al (2008), Chauhan et al (2011), andEswaraiah et al (2012), among others. These TCDs can be used to perform a qualitative analysis of the nature of the extinction by using the relation R c = R n ×(a c /a n ), where R n is the normal extinction law, a c is the slope of the linear fit for the cluster members, and a n is the slope for field stars.…”

Section: Two-colour Diagramsmentioning

confidence: 99%

Probing the anomalous extinction of four young star clusters: the use of colour-excess, main-sequence fitting and fractal analysis

Fernandes

Gregorio-Hetem

Hetem

2012

A&A

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Aims. We studied four young star clusters to characterise their anomalous extinction or variable reddening and asses whether they could be due to contamination by either dense clouds or circumstellar effects. Methods. We evaluated the extinction law (R V ) by adopting two methods: (i) the use of theoretical expressions based on the colourexcess of stars with known spectral type; and (ii) the analysis of two-colour diagrams, where the slope of the observed colour distribution was compared to the normal distribution. An algorithm to reproduce the zero-age main-sequence (ZAMS) reddened colours was developed to derive the average visual extinction (A V ) that provides the closest fit to the observational data. The structure of the clouds was evaluated by means of a statistical fractal analysis, designed to compare their geometric structure with the spatial distribution of the cluster members. Results. The cluster NGC 6530 is the only object of our sample affected by anomalous extinction. On average, the other clusters suffer normal extinction, but several of their members, mainly in NGC 2264, seem to have high R V , probably because of circumstellar effects. The ZAMS fitting provides A V values that are in good agreement with those found in the literature. The fractal analysis shows that NGC 6530 has a centrally concentrated distribution of stars that differs from the substructures found in the density distribution of the cloud projected in the A V map, suggesting that the original cloud was changed by the cluster formation. However, the fractal dimension and statistical parameters of Berkeley 86, NGC 2244, and NGC 2264 indicate that there is a good cloud-cluster correlation, when compared to other works based on an artificial distribution of points.

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Broad-band optical polarimetric studies towards the Galactic young star cluster Berkeley 59

Cited by 30 publications

References 45 publications

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

Multiwavelength Stellar Polarimetry of the Filamentary Cloud IC5146. I. Dust Properties

Probing the anomalous extinction of four young star clusters: the use of colour-excess, main-sequence fitting and fractal analysis

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