18.01.2021

Post-processed I-Band SXDR image of the Sirius field with an exposure time of 180 seconds. The signal from Sirius is not saturated. The cataloged sources are marked in red. The newly detected sources are marked in blue. Center Inset: A faint source with a contrast ratio of 1:100 million.

The night sky is speckled with the light from hundreds of billions of stars within our galaxy. The brightest few thousand of these celestial bodies captivate the human eye and imagination. For astronomers seeking to detect undiscovered stars and, potentially, the planets around them, however, this brightness can be problematic as it may overwhelm the light coming from fainter, nearby objects.

Research from Florida Tech graduate research assistant Sailee Sawant, presented at the 237th meeting of the American Astronomical Society (AAS) on Jan. 15, has demonstrated a remarkable leap forward in the use of a new class of imaging detector, the charge-injection device (CID), to capture extreme contrast ratio (ECR) images needed to overcome the brightness of nearby stars.

In her dissertation, "Extreme Contrast Ratio Imaging of Sirius with a Charge-Injection Device," Sailee reported four key findings:

+ The acquisition of an unsaturated image of Sirius with an exposure time of 180 seconds, which had never been done before.

+ The detection and resolution of previously uncataloged sources, along with Sirius B, without imposing complex operational requirements.

+ The demonstration of a direct, achievable contrast ratio of 1:100 million with the 1.0m Jacobus Kapteyn Telescope in La Palma, Canary Isles. This is a five times improvement over the previous work done with Florida Tech's 0.8M telescope.

+ The success of a simple, cost-effective, yet powerful technique that combines CID imaging and software-based image analysis.

Sawant's work is a continuation of CID and ECR research at Florida Tech that dates to 2014, when a team led by Sawant's advisor, Daniel Batcheldor, at the time head of the Department of Physics and Space Sciences, received a Center for the Advancement of Science in Space grant to test a CID camera on the International Space Station.

In 2016, Batcheldor's research findings demonstrated CIDs have the ability to capture light from objects tens of millions of times fainter than another object in the same image. A year later, the CASIS-funded grant came to fruition, as the camera was demonstrated to function on low-Earth orbit on the space station.

Batcheldor and Sawant's research using CID technology focused on Sirius, the brightest star in our night sky, and its smaller white dwarf companion, Sirius B. Typically, it is challenging to image Sirius B near Sirius' brighter light.

However, using the Jacobus Kapteyn Telescope in La Palma, Canary Isles, CID and ECR technology, and algorithms that increase picture clarity, the researchers were able to easily detect the white dwarf.

Previously uncatalogued stars were also found in the same field as Sirius, potentially providing a sample of interesting new targets for follow up research.

"We took this image and did some data reduction on it, but could see a speck of Sirius B, and I remember Dr. Batcheldor tweeting that we had this raw image from the observatory," Sawant said.

Even with CIDs and ECR making more stars detectable, a lot of work goes into processing the image after it has been captured. Sawant's image analysis methods incorporate wavelet transform algorithms to analyze images at different resolution scales.

Additionally, she has to filter and reconstruct the image and acquire the source information. By doing this, Sawant is able to tell how bright one star is in comparison to another, much fainter one.

Quelle: SD