Visible Emission Line Coronagraph
Recently, scientists at the Indian Institute of Astrophysics (IIA) have collaborated with NASA to estimate the crucial parameters of a coronal mass ejection (CME) by using Visible Emission Line Coronagraph (VELC) payload onboard India’s Aditya-L1 mission.
About Visible Emission Line Coronagraph
The Visible Emission Line Coronagraph (VELC) is a specialized instrument, and the primary payload on India's first solar mission, Aditya-L1, designed to study the solar corona by blocking the Sun's bright disk. It performs simultaneous imaging, spectroscopy, and spectro-polarimetry in visible and infrared wavelengths, providing continuous, high-resolution observations of the Sun's outermost atmosphere.
Key Functions and Objectives
The main purpose of the VELC is to diagnose the physical conditions of the solar corona and related phenomena. Its scientific objectives include:
- Diagnosing Coronal Parameters: Measuring the temperature, velocity, and density of the coronal plasma.
- Studying Coronal Heating and Solar Wind: Helping to understand the mechanisms responsible for the Sun's atmosphere being millions of degrees hotter than its surface, and the acceleration of the solar wind.
- Analyzing Coronal Mass Ejections (CMEs): Investigating the origin, development, and dynamics of CMEs and other large-scale solar transients, which are major drivers of space weather.
- Measuring Coronal Magnetic Fields: Using spectro-polarimetric data (specifically at the 10,747 Å emission line) to map the magnetic field topology of the corona.
Technical Features
The VELC is an internally occulted reflective coronagraph, meaning it uses internal mirrors and an occulter to block the direct sunlight and minimize scattered light, similar to how the Moon blocks the Sun during a total solar eclipse. Key technical aspects include:
- Imaging and Spectroscopy: It provides images of the corona in the continuum (at 5000 Å) and simultaneously obtains spectra in three specific emission lines:
- 5303 Å (Fe XIV): Green line, indicative of very high temperatures.
- 7892 Å (Fe XI): Infrared line.
- 10,747 Å (Fe XIII): Infrared line, also used for magnetic field measurements.
- Field of View (FoV): It observes the corona from very close to the solar limb: 1.05 to 3.0 solar radii .
- High Resolution: It offers better spectral resolution compared to previous space-based visible light coronagraphs, enabling detailed analysis of coronal dynamics.
- Data Acquisition: It uses a multi-slit assembly and a linear scan mechanism to cover the desired field of view and capture detailed spectral profiles.
Significance
The VELC is the first space-based instrument to provide continuous, high-resolution spectroscopic and polarimetric observations of the inner solar corona. This unique capability allows scientists to study the drivers of space weather events like CMEs as they form and accelerate close to the Sun, leading to a better understanding of solar physics and improved space weather forecasting.
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