#### Infrared and Optical Astronomy

The Infrared Astronomy Group specializes in the observational studies of star and planet formation, physics and chemistry of the interstellar medium, the Galactic structure and kinematics of stellar populations in the Galaxy. The group also specializes in astronomi- cal instrumentation for ground-based and space-based (balloon- and satellite-borne) infrared astronomy.

1. ### Star formation and its impact on the ISM in our Galaxy and nearby Galaxies

The primary goals of this program are:

• Understand the local (and subsequently) global conditions which lead to the onset of star formation in molecular clouds
• Study the physical processes and mechanisms that regulate the evolution of the newly born stars
• Impact of the newly born stars on the surrounding molecular cloud since this decides the evolution of the ISM in a galaxy and determines the rate of formation of stars in future

The program involves multiwavelength (optical to radio) continuum and spectroscopic observations using ground- and space-based telescopes. In-house modeling capabilities have also been developed for the interpretation of the data.

2. ### Astrochemistry using spectroscopic observations

In spite of the extremely low number density of particles in the interstellar medium (ISM), a surprisingly large number of molecules have been detected in the outer space. In this program we observe spectral lines from complex molecules and ions in space, both in emission and absorption in the infrared to millimeter wavelengths using space- and ground-based telescopes. The primary goals of this program are:

• Detection of new molecules
• Estimation of density, temperature and abundance of chemical species in dense $(10^5\,\mathrm{cm}^{-3})$ and diffuse $(10^2\,\mathrm{cm}^{-3})$ regions in the matter between the stars (ISM)
• Probing important gas-phase & grain-surface chemical pathways in the rarified environment of the ISM
• Use temperatures and chemical reactions as probes of heating mechanisms viz., stellar photons, dissipation of turbulence, which are of general relevance to our understanding of the ISM evolution and the process of star formation.
3. ### Protoplanetary Disk Evolution & Planet formation

Coagulation of dust plays an important role in the formation of planets and this program studies evolution of protoplanetary disks in order to study physical processes such as grain growth, sedimentation and crystallization. The program obtains observations of infrared spectra of tracers of the onset of planet formation in protoplanetary disks and confronts the state-of-the art models of planet formation in disks.

4. ### Galactic Structure & Stellar kinematics

The primary goal of this program is to investigate in detail the observed ultraviolet (UV) star counts obtained by Galaxy Evolution Explorer (GALEX) vis-a-vis the model simulated catalogues produced by the Besançon model of stellar population synthesis in various Galactic directions, and to explore the potential for studying the structure of our Galaxy from images in multiple near-UV (NUV) and far-UV (FUV) filters of the forthcoming Ultraviolet Imaging Telescope (UVIT) to be flown onboard ASTROSAT.

#### Instrumentation Programs

The group has a long tradition of development of Near and Far infrared instruments for ground and space-based Indian observing facilities. The current programs in instrumentation include development of a Near Infrared imaging camera as well as spectrometers particularly sensitive to the Near infrared wavelengths. Some of the currently operational and under development instruments are:

• ### TIRSPEC

A medium resolution (~1200) spectrometer cum imaging camera, based on a 1024 x 1024 pixel Hawaii-1 PACE array, operating between 1 to 2.5 μm wavelength range, mounted on the 2 metre Himalayan Chandra Telescope (HCT) IAO, Hanle, Ladakh, India. This instrument is operated remotely from CREST, IIA, Hosakote, Bangalore.

• ### TIRCAM2

A closed-cycle cooled imager operating between 1 to 3.7 μm wavelength range, presently being used with IUCAA's 2 metre Girawali Observatory telescope near Pune. The imager has been entirely designed and fabricated in-house. The main highlight is the camera's capability of mapping the Polycyclic Aromatic Hydrocarbon (PAH) emission at 3.3 μm.

• ### TIFR 1 metre FIR balloon-borne telescope

A Far Infrared balloon borne telescope in Cassegrain configuration with a 1 metre diameter primary mirror has been in operation since 1984. The focal plane instrumentation for this telescope have been developed in-house as well as in collaboration with other groups working in Far Infrared Astronomy. Currently a Japanese Fabry-Perot spectrometer tuned to the 158 μm fine-structure transition of C+, one of the major coolants of the ISM, is being used with this telescope. In the near future, a Fabry Perot Spectrometer tuned to 34 μm ([Si II] line) is also planned to be used. This telescope is flown from the TIFR Balloon Facility at Hyderabad .

• ### TIFR-ARIES Near Infrared Spectrometer (TANSPEC)

The group is developing a medium resolution (~3000) near Infrared Spectrometer (TANSPEC) which will be operational between 0.8 to 2.5 μm wavelength range to be used with the upcoming ARIES 3.6 metre telescope at Devasthal, Nainital. This instrument is in the preliminary stages of design.

• ### InfraRed Spectroscopic Imaging Survey

The group is developing a Near infrared optical fibre fed spectrometer for an Indian small satellite mission. The instrument will operate between 1.7 to 6 μm wavelength range and will observe 50% of the full sky including the Galactic Plane during its two year life time. The laboratory model is at present in an advanced stage of assembly.