Among other messengers, the main tool to study the Universe is the light we receive from astronomical objects. For this reason, the techniques used to obtain and process these images are of great relevance.
In this line, a publication led by Nicolás Godoy, PhD student at the Institute of Physics and Astronomy of the University of Valparaíso (UV) and member of Nucleus Millennium of Planetary Formation (NPF), seeks to improve one of the technique used to search for young giant planets around stars other than the Sun. In this study, accepted for publication in the prestigious journal Astronomy & Astrophysics, also participates Johan Olofsson, associate researcher of the NPF and leader of the Max Planck – UV tandem group, and Amelia Bayo, director of the NPF.
This work was carried out in the framework of an international collaboration between the Max Planck Institute for Astronomy – MPIA – and the Geneva Observatory, among many other collaborators located in Europe and America. The collaboration, entitled “ISPY – NaCo Imaging Survey for Planets around Young stars”, aims to search for young sub-stellar objects (e.g. giant gas planets) using the NaCo/VLT instrument of the Paranal Observatory, part of the European Southern Observatory, ESO, located in Chile.
The observational technique, called “high-contrast direct imaging”, uses a mask called a coronagraph to block most of the light from the star, allowing for deeper observations closer to the star. This mask is an area of the camera’s field of view through which virtually no light can pass, and during the observations, we can try to align this mask with the position of the star, by moving different parts, mostly mirrors, of the telescope. In doing so, the instruments are able to detect faint objects around it. In this research, the method is improved taking advantage of the way the data is obtained with this type of mask.
One of the main challenge of post-processing data obtained with high-contrast direct imaging (using a coronagraph) is to determine the position of the star behind the coronagraph. Indeed, since the mask is blocking the star, it is very difficult to know its exact position, while this is a crucial information when processing the observations later on. For this, it is required to select the best images by discarding the poor quality ones. “In this research, we have designed a strategy that allows us to improve the technique of centering and identifying the location of the star behind the mask, so that extra observations and calibrations -requiring additional telescope time- are not needed. In addition, we worked on a new way to identify the best frames, and only select those, that could eventually help to homogenize the use of this technique in different future studies (see image illustrating the note)”, says Nicolás Godoy.
“By making dedicated tests, we demonstrate that the position of the star that we estimate using our approach is very close to its real position on the camera, with good accuracy” he adds.
Amelia Bayo, who is also an academic at the Institute of Physics and Astronomy of the UV, comments that all these processes are achieved by a combination of software and hardware processes that are applied not only during the observations, but, in the case of the software, also a posteriori.
With this method, researchers can know with great precision the position of the star, and not only in observations made with NaCo. Any instrument using the same technique and coronagraph could potentially benefit from this study.
“This post-processing can be used for other instruments because, for example, NaCo is no longer available at the telescope in Paranal, but that does not mean that the method cannot be used for other instruments,” says Amelia Bayo.
This technique is already being applied within the ISPY consortium. “This study opens new windows to improve the quality of the final astronomical images not only for current instruments but also for the vast database and images that have already been acquired with, for example, NaCo/VLT,” says Godoy.
The authors indicate that a new review and search in the databases using the results of this study could be of great help to detect some new planet that, for not having enough precision and/or not having the adequate tools, the previous studies could not find.