Astronomy and Astrophysics Seminars

Importance of UV studies in characterizing very young to old stellar populations

by Dr. Prasanta Kumar Nayak (DAA, TIFR)

Tuesday, June 22, 2021 from to (Asia/Kolkata)
at Zoom link: ( (Meeting ID: 984 0705 5923 Passcode: DAASem22Ju) )
Meeting ID: 984 0705 5923 Passcode: DAASem22Ju
Stellar sources that emit prominently in the UV include young hot populations (O and B type stars)
and relatively older populations such as blue horizontal branch stars (BHB), white dwarf (WD).
Accreting pre-main-sequence (PMS) stars and chromospherically active stars also produce
significant UV emission. However, many of these sources are less prominent in the optical bands,
making it difficult to trace them and characterize them. Therefore, by combining optical data with
UV, we can not only distinguish them but depending on their UV observations, we can also
determine the various stellar properties. In this talk, I will discuss how UV studies can be used to:

(a) Characterise the accretion phenomenon in low-mass pre-main-sequence stars known as T-Tauri stars (TTS), generally categorized into accreting Classical TTS (CTTS) and non-accreting Weakline TTS (WTTS). CTTS are found to have very high UV emission due to their accretion
mechanism, while comparatively less UV excess is found in WTTS due to chromospheric activity.

(b) Find new TTS candidates in the nearby star-forming regions based on their UV excess.

(c) Search for new WD+MS binaries in the solar neighborhood where WD remains hidden in the
optical color-magnitude diagram (CMD). Combing UV data with optical helps us to bring out the
hot WD companions in the UV-optical CMD.

(d) Probe the young star-forming regions in the Small Magellanic Cloud (SMC), which is thought to
be formed due to the recent interaction with the Large Magellanic Cloud (LMC). Age-dating of the
recent star-forming regions will help us to determine the timescale of recent interaction, which will
further help in theoretical modeling of the interaction scenario.