Dr. Kartik Sheth, ALMA, and SKA March 19, 2013Posted by admin in : Astronomy and Astrophysics (ASTRO), Cosmology, Gravitation, and Relativity (CGR) , trackback
by JC Holbrook
National Society of Black Physicists members Eric Wilcots and Kartik Sheth were part of a new initiative to foster radio astronomy collaborations with South African astronomers and students. Last week marked the official inauguration of ALMA, the Atacama Large Millimeter/Submillimeter Array, in the high altitude Atacama desert of Chile, South America. I was able to sit down with Dr. Sheth to discuss the broader issue of radio astronomy and South Africa.
“I think this celebration was the culmination of thirty years worth of work from a lot of different people. The inauguration of the array was a chance for us to celebrate how much hard work has gone into it.” Dr. Sheth said of the inauguration ceremony in Chile. “We started science operations September 30th of 2011. We have been collecting data for over two and a half years, because even with a small ALMA it is still the most powerful [millimeter/submillimeter] telescope in the world.”
Since ALMA is an array of dishes similar to the radio dishes of the Very Large Array in New Mexico, even during construction as each dish was put into place and connected, the astronomers were already using what was available to collect data. Thus, the months of science data collection with ALMA before the official inauguration.
I pointed out, “You were not even there!”
Dr. Sheth laughed, “Only the dignitaries were invited, so a lot of people from the political arena in the twenty-five plus countries that are part of ALMA. President Piñera inaugurated ALMA…For me it doesn’t mean much… but I’m kinda sad that I’m not there because I really wanted to be there. But I knew that I wasn’t going to be invited, so coming here [to South Africa] really was driven by the NASSP deadline for Master’s proposals.” NASSP is the National Astrophysics and Space Sciences Programme in South Africa. In 2010, I began writing a book about NASSP. The program is a dramatic success story about educating underrepresented groups in astrophysics and space sciences. NASSP include one honor year and a two year masters of science degree. Nearly all NASSP students are funded by the program.
Dr. Sheth explained, “The idea is to foster bridges between the faculty here that are taking on students who eventually want to work with MeerKat and SKA. But MeerKAT and SKA are not built, yet. So, what we would really like the faculty to do is to think about including radio data from existing telescopes and NRAO operates four of them.”
The SKA is currently under construction, yet the South African astronomy students need to learn everything about radio astronomy and the analysis of radio data. Dr. Sheth along with other American radio astronomers is here to encourage South African astronomers and their students the opportunity to learn by working with the existing facilities and their archival data. The four facilities are ALMA, the Robert C. Byrd Greenbank telescope a single dish in West Virginia, the Jansky Very Large Array (JVLA or EVLA) which is the enhanced VLA in New Mexico, and the Very Large Baseline Array (VLBA) which is spread across the Northern Hemisphere. Thus, the visit before the NASSP deadline for submitting Masters of Science thesis proposals. Dr. Sheth hopes that a few NASSP students will propose radio astronomy projects including using NRAO facilities for their Masters work.
According to Dr. Sheth the JVLA is the Northern Hemisphere equivalent of what MeerKat will be. MeerKat is the precursor to the SKA, the Square Kilometer Array. It is a new state of the art radio observatory currently being built in South Africa. The SKA array itself will consist of 3000 dishes spread across nine African countries: South Africa, Namibia, Botswana, Mozambique, Madagascar, Mauritius, Zambia, Ghana, and Kenya. The SKA Africa headquarters are in Cape Town, South Africa, and they will be coordinating all of the African construction. A question I thought would be uppermost in the minds of South Africans was: Will ALMA be competition for SKA?
His response, “No, not at all. ALMA operates at higher frequencies than what the SKA will operate at. They are not looking at the same part of the electromagnetic spectrum but they will be looking at the same type of objects. EVLA is a mini version of SKA. With the SKA, it will be observing thermal emission and synchrotron emission from sources…” In an email he added, “We are looking at electrons energy as they cool around star forming regions or zip around magnetic fields. So you can get a real idea of the magnetic field that pervades the Milky Way and with the SKA across cosmic time. ALMA cannot really look at atomic gas unless its at very high red shift (i.e. the lines are red shifted into the regime that ALMA can observe) and only using atomic gas tracers like ionized carbon, nitrogen, or oxygen. ALMA cannot look at the atomic hydrogen gas which is emitting in the wavelengths that MeerKat and SKA will work at. So SKA & Meerkat are looking at the atomic gas from which molecular gas forms. And the molecular gas is what ALMA looks at which from stars form. And the stars are what HST and JWST look at. So it is a nice transition. Together these are giving you the full picture of what the universe looks like. Additionally there is a lot about magnetic fields and transient phenomena — these are also MeerKat and SKA’s core strengths. For instance, these will be excellent instruments for looking at the timing of pulsars.”
Trying to put it altogether I asked, “So, anything that is hot and has electrons moving around will be able to be studied by SKA?”
Kartik Sheth clarified, “No, I wouldn’t call it ‘hot’. The atomic gas is quite cold as well. It is hotter than the molecular gas but not hot compared to stars.”
As a student of astronomy, I had always had a fascination with the connection between wavelengths of light or color, physical properties, chemistry, and celestial bodies. Planetary nebulae, which are mentioned in my last Vector blog, in visible light appear greenish in color. The color is the result of a specific atomic transition in the oxygen atom that occurs under very low density conditions. First the oxygen has to be ionized twice, i.e. it has to have lost two electrons, then it is through collisions that the transitions producing the characteristic green lines emit. A rule-of-thumb temperature for planetary nebulae is 10,000 degrees Kelvin. Thus, if there is a celestial body that appears ‘green’ in visible light you can conclude that it might include oxygen especially if it is a nebula which tends to have low density and it should be around 10,000 degrees Kelvin. Hydrogen is also found in planetary nebulae and the strongest transition line, known as H-alpha, occurs when its electron goes from an excited state to a less excited state releasing energy in the form of red light.
In the case of ALMA and SKA, they are probing two different sections of the electromagnetic spectrum similar to studying green light or red light. In the fullness of time, SKA will cover the same wavelengths and types of celestial bodies as the EVLA but focused on the Southern sky rather than the Northern, but also be more sensitive revealing more physical details. ALMA will add to our understanding of the same region of the sky but is studying different physical properties of celestial bodies. Both will add to our understanding of the Milky Way and the Universe.