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Determination of the chromospheric quiet network element area index and its variation between 2008 and 2011

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Research in Astronomy and Astrophysics 2012年第2期12卷 201-211页

作者： Jagdev Singh ravindra belur Selvendran Raju Kumaravel Pichaimani Muthu Priyal Thambaje Gopalan Priya Amareswari Kotikalapudi Indian Institute of Astrophysics Koramangala

In general, it is believed that plages and sunspots are the main contribu- tors to solar irradiance. There are small-scale structures on the Sun with intermediate magnetic fields that could also contribute to solar irradiance, but it has not yet been quantified how many of these small scale structures contribute and how much this varies over the solar cycle. We used Ca II K images obtained from the telescope at the Kodaikanal observatory. We report a method to separate the network elements from the background structure and plage regions, and compute the changes in the network element area index during the minimum phase of the solar cycle and part of the as- cending phase of cycle 24. The measured area occupied by the network elements is about 30% and the plages cover less than 1% of the solar disk during the observation period from February 2008 to 2011. During the extended period of minimum activity, it is observed that the network element area index decreases by about 7% compared to the area occupied by the network elements in 2008. A long term study of the network element area index is required to understand the variations over the solar cycle.

关键词： Sun: network - Sun: Ca-K - Sun: solar cycle

On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158

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Research in Astronomy and Astrophysics 2014年第2期14卷 207-220页

作者： Ankala Raja Bayanna Brajesh Kumar Parameswaran Venkatakrishnan Shibu Kunchandy Mathew belur ravindra Savita Mathur Rafael A Garcia Udaipur Solar Observatory Physical Research LaboratoryDewaliBadi RoadUdaipur 313 004India Indian Institute of Astrophysics II BlockKoramanglaBangalore 560034India Space Science Institute 4750 Walnut Street Suite#205BoulderCO 80301USA Laboratoire AIM CEA/DSM-CNRSUniversit'e Paris 7 DiderotIRFU/SApCentre de Saclay91191Gif-sur-YvetteFrance

The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk. The first major flare （of class X2.2） of the current solar cycle occurred in this active region on 2011 February 15 around 01：50 UT. We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager （HMI） instrument onboard Solar Dynamics Observatory to examine the photospheric velocity and magnetic field changes associated with this flare. The HMI instrument provides high-quality Doppler and magnetic maps of the solar disk with 0.5＂ spatial scale at a cadence of 45 s along with imaging spectroscopy. We have identified five locations of velocity transients in the active region during the flare. These transient velocity signals are located in and around the flare ribbons as observed by Hinode in the Ca II H wavelength and the footpoints of hard X-ray enhancement are in the energy range 12-25 keV from RHESSI. The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations. Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength, Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.

关键词： Sun: activity -- Sun: sunspot -- Sun: flares -- Sun: spectroscopy --Sun: velocity and magnetic fields

Full-disk synoptic observations of the chromosphere using Hα telescope at the Kodaikanal Observatory

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Research in Astronomy and Astrophysics 2016年第8期16卷 79-88页

作者： belur ravindra Kesavan Prabhu Komandur Elayaveilli Rangarajan Bagare Shekar Singh Jagdev Kemkar Madan Mohan Paul Lancelot Koyipurathu Chellappan Thulasidharen Francis Gabriel Raju Selvendran Indian Institute of Astrophysics Ilnd BlockKoramangalaBengaluru-560034India

This paper reports on the installation and observations of a new solar telescope installed on 2014 October 7 at the Kodaikanal Observatory. The telescope is a refractive type equipped with a tunable Lyot Hα filter. A CCD camera with size 2k ×2k acquires images of the Sun and has a pixel size of 1.21″ pixel^-1 and a full field-of-view of 41＇. The telescope is equipped with a guiding system which keeps the image of the Sun within a few pixels throughout the observations. The FWHM of the Lyot filter is 0.4A and the filter is motorized, capable of scanning the Hα line profile at a smaller step size of 0.01 A. Partial-disk imaging covering about 10＇ is also possible with the help of a relay lens kept in front of the CCD camera. In this paper, we report the detailed specifications of the telescope, filter unit, the installation, observations and the procedures we have followed to calibrate and align the data. We also present preliminary results with this new full-disk telescope.

关键词： Sun: chromosphere-- instrumentation miscellaneous -- telescopes solar telescope -- objectSun -- observations Hα

ERRATUM: “Determination of the chromospheric quiet network element area index and its variation between 2008 and 2011” (RAA, Vol. 12, p.201 [2012])

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Research in Astronomy and Astrophysics 2012年第4期12卷 472-472页

作者： Jagdev Singh ravindra belur Selvendran Raju Kumaravel Pichaimani Muthu Priyal Thambaje Gopalan Priya Amareswari Kotikalapudi Indian Institute of Astrophysics Koramangala Bengaluru-560 034 India

As a result of the authors＇ error, the paper ＂Determination of the chromospheric quiet network element area index and its variation between 2008 and 2011＂ by Singh, J. et al. （RAA, Vol. 12, p.201 [2012]） contains errors in page 206. In the original article, the top right and bottom images were inadvertently interchanged in Figure 5. The correct sequence of images is shown in this erratum. Figure caption and details about the images remain unchanged.

关键词： Sun:network—Sun:Ca-K—Sun:solar cycle