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Bright UV light source tested by NGC 4590, over 1,400 stars found at various stages of evolution

2012 view of NGC 4590 from the wide field camera of Hubble’s advanced camera for surveys. Credits: Kumar et al. , 2022.

Using the Indian Astrosat spacecraft, astronomers inspected the bright UV (UV) light sources of globular clusters known as NGC 4590 and identified more than 1,400 stellar objects showing various evolutionary states. This study was published on February 8th at arXiv.org.


Globular clusters (GCs) are tightly coupled groups of stars that orbit the galaxy. Astronomers recognize them as natural laboratories that enable research into the evolution of stars and galaxies. In particular, Globular cluster The origin of GC appears to be closely related to the period of intense star formation, which can help researchers better understand the history and evolution of early galaxy formation.

The GC is a great place to solve and observe the characteristics of individual stars at different stages of evolution. Studies show that light sources with an effective temperature above 7,000 K primarily contribute to the ultraviolet (UV) radiation of the GC. Such UV bright sources in the GC can be identified, for example, as a blue horizontal branch (BHB), a very blue horizontal branch (EHB), or an asymptotic giant branch (pAGB).

At a distance of about 33,900 Light year, NGC 4590 (also known as Messier 68) is a very low metal galaxy GC in the northern hemisphere of the Milky Way.The get together Is estimated to be 11.2 billion years ago, and its line of sight is at the 0.05 level. Previous observations of NGC 4590 have shown that it hosts a significant number of BHBs and red horizontal branch stars (RHBs).

Hope to get more insight into the hot star population of NGC 4590, our team Astronomer The cluster, led by Ranjan Kumar of the National Institute of Technology in Lulu Kera, India, decided to investigate with AstroSat’s UV Imaging Telescope (UVIT).

“We used UV Optical Colors-Magnitude Diagram (CMD) to identify and characterize the causes of various evolutionary stages: the blue horizontal branch star (BHB), the very blue horizontal branch star (EHB). ), Blue Struggler (BS), Variable Star, etc. ”The researchers wrote in their papers.

In general, with UVIT observations using three far-ultraviolet (FUV) and three near-giant (NUV) filters, the team has 57 BHBs, 11 RHBs, 246 red-giant branch stars (RGB), 140. Subgiant Branch Star (SGB), 254 Main Sequence Stars (MSTO), 626 Main Sequence (MS) Stars, 41 RR Lyra, 31 Blue Struggler Stars (BS), 2 SX Phoenicis variable star (SXPhes), and one asymptotic giant branch (AGB) star.

The study also detected two new FUV bright sources in the core of the NGC 4590. One of them is EHB, but the nature of the second light source remains unknown. Astronomers assume that this peculiar source is in its post-blue hook evolutionary stage or white dwarf (WD) stage.

Researchers have found that the heavier young BS of NGC 4590 is concentrated in its center, while older, heavier stars of this type are distributed throughout the cluster. Astronomers added that the normalized radial distribution of BS stars appears to be bimodal.

In terms of the properties of the identified stars, BHB is two to five times as large as the Sun and has a mass in the range of 0.6 to 0.65. Solar mass.. The effective temperature of these stars was calculated to be between 7,250 and 10,500K.

For the RHB, the smallest has a radius of about 7.72 solar radius and the largest is about 10.42 times larger than our sun. The mass of RHBs has been estimated to be at the level of solar masses between 0.65 and 0.7, but their effective temperature is probably around 6,000K.

The identified BS stars have a radius of 0.93 to 3.76, a mass of 0.84 to 1.26, and an effective temperature in the range of 5,750 to 9,000K. Researchers were also able to determine these ages. PerformerTurned out to be 1.5-10 billion years old.

To summarize the results, the authors of the paper found that NGC 4590 has a dynamic age of approximately 423 million years and is dynamically one of the youngest clusters of middle-aged galactic GCs. I did. They added that further research on this cluster is needed to further shed light on the characteristics of other stellar groups in this GC.


Open cluster NGC188 explored in AstroSat


For more information:
Ranjan Kumar et al, Study of UV bright light source for globular cluster NGC4590 using UV imaging telescope (UVIT) observations. arXiv: 2202.03981v1 [astro-ph.GA], arxiv.org/abs/2202.03981

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Quote: Bright source of UV light tested by NGC 4590, over 1,400 stars found at various stages of evolution (February 15, 2022) https: //phys.org/news/2022-02-ultraviolet-bright Obtained from -sources-ngc on February 15, 2022. -stars.html

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Bright UV light source tested by NGC 4590, over 1,400 stars found at various stages of evolution

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