Data archive of the multi-channel infrared solar spectrograph(2001–2015)

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Data archive of the multi-channel infrared solar spectrograph(2001–2015)

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Data archive of the multi-channel infrared solar spectrograph(2001–2015)

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            Data source: Chinese Science Citation Database(CSCD)

Data Archive of the Multi-channel Infrared Solar Spectrograph(2001–2015)

Yang Zherui1,Du Qiusheng1, Li Hui1, Gao Na1, Liu Liang1*

1.Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, P. R. China

* Email: LiangLiu@pmo.ac.cn

Abstract: The observation and study of solar spectrum can help us to know physical parameters, such as the plasma velocity, electron temperatures, electron density, etc., of the line formation layers of solar atmosphere, because different spectral lines are formed in different layers of the solar atmosphere. Simultaneous observations in multiple lines are important for us to establish and testify atmospheric models. The Multi-channel Infrared Solar Spectrograph (MISS) at Purple Mountain Observatory records slit-jaw Hα monochromatic images and obtains spectral data in three spectral lines, namely, the Hα (6563Å) line, the CaII 8542Å line and the HeI 10830Å line. From MISS observation data, we can get information about the intensity at the line center, line wings and nearby continuum of the three lines, as well as line profiles and plasma velocity. The collected observation data of MISS span a period from 2001 to 2015.

Keywords: MISS; slit-jaw Hα image; spectral data; IDL

Database Profile

Chinese title

多通道近红外太阳光谱仪数据集

English title

Data archive of the Multi-channel Infrared Solar Spectrograph (2001 – 2015)

Corresponding author

Liu Liang (liangliu@pmo.ac.cn)

Data author(s)

Yang Zherui, Du Qiusheng, Li Hui,Gao Na,Liu Liang

Time range

2001 – 2015

Spatial scope

Solar disk and limb

Spatial resolution

0.375” of heliographic coordinate system

Data volume

199,000 MB

Data format

.fits, .raw, .img, .tif

Data service system

 

Source(s) of funding

Astronomy Committee of CAS (Special Fiscal Funds for Astronomy 2015); “Observation and Maintenance of the Solar Spectrograph at Purple Mountain Observatory”

Database composition

The archive consists of: slit-jaw Hα images during 2001 – 2005, 2010 – 2015; spectral data of Hα (6563Å) line during 2001 – 2015; spectral data of CaII 8542Å line during 2001 – 2004, 2006 – 2015; and spectral data of HeI 10830Å line during 2001 – 2004, 2012 – 2014.

1. Introduction

Radiation during solar activities will activate transitions of atoms from high to low energy levels in the atmosphere, causing emissions of photons in specific wavebands. Multi-channel solar spectrum help determine the physical parameters of different layers of the solar atmosphere. Continuous observations of solar activities, such as active prominence, filament and solar flare, are important for studies of the triggering mechanism of solar activity1.

The MISS at Purple Mountain Observatory was built in 1976. After several updates and improvements since 1986, a new MISS started to conduct spectral observation of solar flare in the Hα, CaII 8542Å and HeI 10830Å lines. We make routine observation of the slit-jaw Hα image, and monitor solar activities by scrutinizing the image. Once any solar flare is found, we start observation in the three lines. The observed spectral data are corrected for dark-current, flat-field and are then stored in FITS format. The data archive contains spectral data of the three lines and slit-jaw Hα images obtained from 2001 to 20152.

2. Data collection and processing

The MISS at Purple Mountain Observatory uses Apogee AP7p CCD to record the spectrograms (changed to XenICs infrared camera for the HeI 10830Å line) and TM860 commercial CCD camera as the slit-jaw image detector (changed to ImperX CCD from 2010 and CoolSnap CCD from 2014, both from the Princeton Instruments), so that all the data are in digital format3. During the observation, we monitor solar activities like solar flares by scrutinizing the slit-jaw Hα images. Once any solar activities are detected, simultaneous observation of the Hα, CaII 8542Å and HeI 10830Å lines will begin and raw data are collected and stored. After routine observation, we generally record the dark-current. The flat-field data are obtained at a regular interval. Observed raw data are corrected for dark-current and flat-field, and the preprocessed data are archived.

2.1 Solar slit-jaw Hα images

MISS exploits a Daystar Hα filter with a passband of 0.5Å to get the solar slit-jaw Hα images.

MISS uses a typical slit-jaw system. Sunlight passing through the slit feeds the spectrograph, while that reflected by the mirror feeds the Daystar filter system and forms the so-called slit-jaw Ha image, which is a partial image of the solar disk due to the limited field-of-view (FOV). We generally start our observation with the slit-jaw system to monitor activities on the Sun by moving the solar image crossing the slit slowly. In this case, the cadence of slit-jaw image is 0.5 to 3 seconds and the images are stored in IMG, RAW or TIF format depending on the detector in use. We start spectroscopic observations once the observer finds any precursors of activities, such as small-scale brightening. The slit-jaw are mainly used to determine the locations of the spectroscopic observation by comparing the obtained image with co-temporal observations from other instruments in Ha or white light.

We archived the slit-jaw Hα image data taken in the time periods 2001 – 2005 and 2010 – 2015. The files for 2001 – 2005, 2011 – 2013 and 2014 – 2015 are named in the format “Ha + yyyymmdd_hhmmss.img”, “Ha + yyyymmdd_hhmmss.raw” and “Ha + yyyymmdd_hhmmss.tif”, respectively, where “yyyy” stands for year, “mmdd” for month and day and “hhmmss” for hour, minute and second when the observation takes place. For example, the file “Ha20130514_004110.raw” stores the slit-jaw images obtained on May 14, 2013 at 00:41:10 UT. The slit-jaw Hα images before and after 2002 March 20 have a dimension of 143 by 143 and 192 by 143 pixels, respectively.

2.2 Multi-channel spectral data

When the spectroscopic observations begin, the observer moves the solar image by adjusting the second mirror of coelostat to select the appropriate target area for the observation from the slit-jaw Hα image where solar activities, such as flares, are most likely to take place. We chose the Hα line, the CaII 8542Å line and the 10830Å line for spectroscopic observation of MISS because these lines have their own characteristics and can be easily found in emission. The spectroscopic data are stored generally in FITS format except that for the HeI 10830Å data after 2012, which are in PNG format due to the change of the detector.

The dark-current and flat-field have their influence on originally recorded data that reflects the influence of observation environment and the pixel response non-uniformity of the CCD in use.  The data of dark-current are related to observing conditions, such as the ambient temperature, humidity, and scattering light in the observation room. Therefore, routine observations and flat-field observations are often followed by dark-current observation. Raw data need to be corrected for dark-current and flat-field. The code used to make these correction is named Flaten.pro4 and written in IDL by researcher Li Hui, which can be found at: . The program corrects for dark-current, flat-field, scattered light and instrumental profile. Normally, the file for flat-filed observation has the same convention as the spectroscopic observations but with a prefix “F”, indicating flat-field file. Most of the data are in FITS format. The IDL program is able to deal with the data in FITS format.

After correcting for the dark-current, flat-field, scattered light and instrumental profile, we add a prefix “DF” to the file name of the spectroscopic data. For example, the file “DFHa20031012_034040.fits” is the data of Hα line observed on October 12, 2003 at 03:40:40 UT. Data for the Hα line and the CaII 8542Å line are stored in FITS format. The data taken during 2001 – 2004 for the HeI 10830Å line are in FITS format while those taken during 2012 – 2014 are in PNG format. 

3. Description of sample data

3.1 Slit-jaw Hα images

The slit-jaw Hα image data are stored in RAW, IMG or TIF format, with a dimension of either 192 by 143 or 143 by 143 as mentioned above. The files are named in the aforementioned convention. However, the files are sometimes named in the format “slit” + (*) + “serial number” or “image” + “serial number”, where (*) can be “A”, “B” or “C”.

Figure 1, with the file name “20141222_043751.tif”, shows the slit-jaw Hα image taken on December 22, 2014.

Fig. 1  The slit-jaw Hα image for December 22, 2014 04:37:51 UT

3.2 Spectral data

All spectral data of Hα and CaII 8542Å lines and data of the HeI 10830Å line taken before 2005 are stored in FITS format. The files are named in the above-mentioned convention, namely “line code” + “yyyymmdd” + “_” + “hhmmss” + “.” + “extension”. The “line code” is “Ha” for the Hα line, “Ca” for the CaII 8542Å line and “He” for the HeI 10830Å line. The file consists of the FITS header and the image data. The FITS header records the parameters related to the observation. The data are a two-dimensional array of 512 ´ 127. The pixel dispersion of MISS for HeI 10830Å , CaII 8542Å and Hαlines are 0.04776Å, 0.05113Å and 0.05453Å, respectively. The spatial resolution in the direction of the slit is 0.375" per pixel, which means that each pixel in Y-axis represents 0.375" on the solar disk.

Take the file “Ha20021110_031135.fit” (obtained on November 10, 2002) as an example. The FITS header is as follows:

 

As usual, the FITS header gives information related to the observation, such as the image dimension, data type, observation date and time, instrument, detector, institute location, exposure time, detector temperature, information of data processing, etc.

The images have 512 by 127 pixels with integer type. Due to the large data volume, we select the data in Row 10 and Columns 1 – 100, as shown by Table 1. 

Table 1  Data in Row 10 and Column 1100 of the file “Ha20021110_031135.fit”

4. Quality control and assessment

The slit-jaw Hα images need to be bright and clear, which sets some requirements to the CCD camera. To verify the image, we compared our slit-jaw image with Ha or white-light images from other ground-based or space-borne instruments (e.g., the Michelson Doppler Imager (MDI) onboard Solar and Heliospheric Observatory (SOHO)). During the verification, we adjusted the location and roll angle of the slit-jaw Hα image to ensure that some significant features, such as sunspots, of the slit-jaw Hα image completely overlapped those in the corresponding area of the images from other instruments.

Instrument failure could lead to invalid data. One can use the IDL program DISPLAY_OBS to plot the spectral profile and check the validity of the spectral data.

5. Data value

The MISS can conduct simultaneous spectroscopic observations in the Hα, CaII 8542Å and HeI 10830Å lines with a cadence of about 9 s on average. The near infrared HeI 10830 line is formed in the high chromosphere and low transition region5. Due to the limitation of detecting technology, spectroscopic observation in the near infrared waveband is rare. There are only two installations capable of carrying out simultaneous observations in the three lines – the MISS of our observatory and the Solar Tower in Nanjing University6. Spectroscopic observations at each have their own features. The MISS makes observations in a sit-and-stare mode with higher temporal resolution. Thus the data are suitable for study of the evolution of solar activities. The Solar Tower in Nanjing University observes in scan mode with a lower temporal resolution. The data can be used to study the 2D spectroscopic properties of solar activities. So the two solar spectrographs are complementary to each other.

Different spectral lines are formed in different layers of solar atmosphere. Data observed simultaneously from multiple lines can inform us of the physical parameters of different layers of the solar atmosphere, which are important in establishing and testifying solar atmosphere models7.

6. Usage notes

The obtained multi-channel spectroscopic data can be processed and analyzed by an appropriate code written in any computer language8, such as the IDL program DISPLAY_OBS9, which can be downloaded at: . It is used to display and analyze the data in FITS or IMG format. The data in PNG format could be opened and handled with any picture processing code or software.

Figures 2 – 4 below show the Hα, CaII 8542Å and HeI 10830Å spectrograms taken on October 12, 2003 with dark-current and flat-field corrected (DFHa20031012_031116.fits, DFCa20031012_031145.fits and DFHe20031012_031146.fits).

Figure 2  Hα spectrogram observed on October 12, 2003 at 03:11:16 UT

Figure 3  CaII 8542Å spectrogram observed on October 12, 2003 at 03:14:45 UT

Figure 4  HeI 10830Å spectrogram observed on October 12, 2003 at 03:11:46 UT

We need to know the heliocentric coordinates of the observation target of the spectroscopic data to conduct relevant study of solar activities. We can get this information by matching the slit-jaw Hα images with the Ha or white-light images from other ground-based or space-borne instruments, for example, with the MDI intensity image. The slit-jaw Hα image and the MDI intensity image were carefully aligned by virtue of common features such as sunspots. Since the MDI intensity image has already been calibrated for the heliocentric coordinates, we can find the exact coordinates of the slit-jaw Hα image by this way. The overlapping can be achieved by shifting and rotating the slit-jaw Hα image. The program for overlapping (i.e., mdi_slit)10 can be downloaded at: .

Here we give an example to demonstrate the process. The selected slit-jaw Hα image (Ha20021109_191236.img) and MDI intensity image are shown in Figures 5 and 6 below, respectively.

Figure 5  The slit-jaw Hα image observed on November 9, 2002 at 19:12:36 UT

Figure 6  MDI intensity gram observed close in time to the image in Figure 5

By adjusting the parameters of the program, shifting and rotating the slit-jaw Hα image, one can match the selected features of the slit-jaw image with that in the MDI intensity image. The result is as shown in Figure 7. The white lines are contours of the MDI intensity image. When the profiles of dark points (sunspot) of the slit-jaw Hα image overlap the contours, the coordinates of the slit-jaw Hα image can then be retrieved. Values of X-axis and Y-axis of the slit are the heliocentric coordinates of spectroscopic data.

Figure 7  Result of using the sunspots in MDI intensity image to find the coordinates of the slit-jaw Hα image and corresponding spectroscopic data

Acknowledgments

This project was supported by Purple Mountain Observatory and Computer Network Information Center, CAS.

References

1. GanW, Li Y, Li H et al. A solar flare scenario based on multi-wavelength observations, Multi-wavelength investigations of solar activity. Proceedings of the International Astronomical Union 223 (2004): 623 – 624.

2. Li H, You J, Du Q et al. Multi-wavelength observation results of the C5.6 Limb Flare of 1 August 2003. Solar Physics 225(2005): 75 – 90.

3. Li H, You J, Wu Q et al. Updated infrared solar spectrograph at Purple Mountain Observatory. Chinese Physics Letters 19(2002): 742 – 744.

4. Li H. IDL program Flaten.pro, 2003. Available at: .

5. Ding M, Li H & Fang C. On the formation of the HeI 10830Å line in a flaring atmosphere. Astronomy & Astrophysics 432(2005): 699 – 704.

6. Fang C & Huang Y. The solar tower telescope of Nanjing University and its multiple solar spectrograph. Acta Astronomica Sinica 24(1983): 189 – 195.

7. Li H, Li J, Fang C et al. A multi-wavelength study of the 3B/X1.2 flare observed on 2003October 26. Chinese Journal of Astronomy and Astrophysics 5 (2005): 645 – 664.

8. Li H, You J, Yu X et al. Multi-wavelength observations of a flare spray and CME of 1 October 2001.  Astronomy & Astrophysics 391(2002): 741 – 748.

9. Li H. IDL program DISPLAY_OBS.pro, 2006. Available at: .

10. Li H. IDL program mdi_slit.pro, 2003. Available at: .

Data citation

Yang Z, Du Q, Li H et al. Data archive of the Multi-channel Infrared Solar Spectrograph (2001 – 2015).  Science Data Bank, DOI:10.11922/sciencedb.590.23

Authors and contributions

Yang Zherui, Assistant Engineer; research area: computer science. Contribution: Web development and database design.

Du Qiusheng, Assistant Professor; research area: astrophysics. Contribution: data scanning and retrieval.

Li Hui, Professor; research area: solar physics. Contribution: program design and data processing.

Gao Na, Engineer; research area: computer science. Contribution: project applying.

Liu Liang, Professor; research area: computer science. Contribution: project organization.

 

 

How to cite this article: Yang Z, Du Q, Li H et al. Data archive of the Multichannel Infrared Solar Spectrograph (2001 – 2015). China Scientific Data 2 (2016), DOI: 10.11922/csdata.590.2015.0019

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