A multiwavelength polarimetric study towards the open cluster NGC 1893

Eswaraiah, Chakali; Pandey, A. K.; Maheswar, G.; Medhi, Biman J.; Pandey, J. C.; Ojha, D. K.; Chen, W. P.

doi:10.1111/j.1365-2966.2010.17780.x

Cited by 45 publications

(46 citation statements)

References 52 publications

(98 reference statements)

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“…If the wavelength dependence of the polarization is well represented by the Serkowski law, σ 1 should not exceed 1.5 because of the weighting scheme. A higher value (>1.5) could be indicative of intrinsic stellar polarization (Waldhausen et al 1999;Feinstein et al 2008;Eswaraiah et al 2011Eswaraiah et al , 2012, and references therein). The rotation of polarization angle with wavelength ( ) also indicates an intrinsic polarization or a change of λ max along the line of sight (Coyne 1974;Martin 1974).…”

Section: Determination Of Distance To L1570mentioning

confidence: 97%

“…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: Determination Of Distance To L1570mentioning

confidence: 97%

Section: Polarimetrymentioning

confidence: 99%

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

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%

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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“…Given that the reddening law toward the neighboring clusters NGC 1893 and Stock 8 turned out to be normal (Jose et al 2008;Eswaraiah et al 2011;Lim et al 2014b), we assumed that the foreground reddening law in the direction of NGC 1931 was likely to be normal. In the lower panels of Figure 9, the color excess ratios of the members show a significant deviation from the normal reddening law.…”

Section: Reddening and The Reddening Lawmentioning

confidence: 99%

The Sejong Open Cluster Survey (Sos). Iv. The Young Open Clusters NGC 1624 and NGC 1931

Lim

Sung

Bessell

et al. 2015

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Young open clusters located in the outer Galaxy provide us with an opportunity to study star formation activity in a different environment from the solar neighborhood. We present a UBVI and Hα photometric study of the young open clusters NGC 1624 and NGC 1931 that are situated toward the Galactic anticenter. Various photometric diagrams are used to select the members of the clusters and to determine the fundamental parameters. NGC 1624 and NGC 1931 are, on average, reddened by E B V ( ) á -ñ = 0.92 ± 0.05 and 0.74 ± 0.17 mag, respectively. The properties of the reddening toward NGC 1931 indicate an abnormal reddening law (R V,cl = 5.2 ± 0.3). Using the zero-age main sequence fitting method we confirm that NGC 1624 is 6.0 ± 0.6 kpc away from the Sun, whereas NGC 1931 is at a distance of 2.3 ± 0.2 kpc. The results from isochrone fitting in the Hertzsprung-Russell diagram indicate the ages of NGC 1624 and NGC 1931 to be less than 4 and 1.5-2.0 Myr, respectively. We derived the initial mass function (IMF) of the clusters. The slope of the IMF ( NGC 1624 G = −2.0 ± 0.2 and NGC 1931 G = −2.0 ± 0.1) appears to be steeper than that of the Salpeter/Kroupa IMF. We discuss the implication of the derived IMF based on simple Monte-Carlo simulations and conclude that the property of star formation in the clusters does not seem to be significantly different from that in the solar neighborhood.

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A multiwavelength polarimetric study towards the open cluster NGC 1893

Cited by 45 publications

References 52 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

The Sejong Open Cluster Survey (Sos). Iv. The Young Open Clusters NGC 1624 and NGC 1931

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