Connecting Molecular Clouds to Clustered Star Formation using Interferometry

Stars are commonly formed in clusters in dense regions of interstellar medium called molecular clouds. In this thesis, we improve our understanding of the physics of star formation through multiple experiments involving interferometry. We use CARMA observations of filaments in Serpens and Perseus molecular clouds to study their morphology and kinematics using dense gas tracers. The observations are compared against predictions from simulations to explain how filaments form and evolve to form stars. Ammonia inversion transitions data is obtained from VLA observations of the NGC 1333 molecular cloud. From this data, we derive temperature, structural and kinematic information about the gas participating in star formation on scales from 2 parsec to 0.01 parsec, thereby connecting the large scale gas and dust structure to individual protostellar envelopes. These observations from ground-based arrays are complemented by the development of the Balloon Experimental Twin Telescope for Infra-red Interferometry (BETTII). This pioneering instrument performs Michelson interferometry along with Fourier Transform Spectroscopy, thereby providing sub-arcsecond angular resolution and spectroscopic capabilities at far-infrared wavelengths 30-100 microns. Using this capability, BETTII will study the dusty envelopes around protostars in clustered star forming regions. The instrument development is a component of the thesis with focus on the optics designing, evaluation and alignment for the completed and upcoming flights. We discuss how the optical system mitigates the challenges of phase control for such a balloon borne interferometer. Further, interferometric simulations of BETTII observations are carried out to investigate how well these observations can constrain the defining parameters of protostars

Morphology and Kinematics of Filaments in the Serpens and Perseus Molecular Clouds

We present H13CO+ (J=1-0) and HNC (J=1-0) maps of regions in Serpens South, Serpens Main and NGC 1333 containing filaments. We also observe the Serpens regions using H13CN (J=1-0). These dense gas tracer molecular line observations carried out with CARMA have an angular resolution of ~7", a spectral resolution of ~0.16 km/s and a sensitivity of 50-100 mJy/beam. Although the large scale structure compares well with the Herschel dust continuum maps, we resolve finer structure within the filaments identified by Herschel. The H13CO+ emission distribution agrees with the existing CARMA N2H+ (J=1-0) maps; so they trace the same morphology and kinematics of the filaments. The H13CO+ maps additionally reveal that many regions have multiple structures partially overlapping in the line-of-sight. In two regions, the velocity differences are as high as 1.4 m/s. We identify 8 filamentary structures having typical widths of 0.03-0.08 pc in these tracers. At least 50% of the filamentary structures have distinct velocity gradients perpendicular to their major axis with average values in the range 4-10 km/s/pc. These findings are in support of the theoretical models of filament formation by 2-D inflow in the shock layer created by colliding turbulent cells. We also find evidence of velocity gradients along the length of two filamentary structures; the gradients suggest that these filaments are inflowing towards the cloud core.Comment: 30 pages, 16 figure

Lessons Learned from the Investigation of an Anomalous Termination of BETTII

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) mission launched from Palestine, Texas in June 2017. After an exciting launch and successful cruise, the BETTII gondola suffered an anomalous event at termination. BETTII separated from its parachute and free-fell 136,000 feet into the west Texas desert. This event was classified as a "close-call" and investigated as such. We present here the recovery effort required to find the payload and extract the payload from its impact site. We also present lessons learned from the event and results from the investigation, the design for the next BETTII gondola, and a path forward for return to flight

A Dispersive Backend Design for the 'Double-Fourier' Interferometer BETTII

BETTII (Balloon Experimental Twin Telescope for Infra-red Interferometry) is designed to provide high angular resolution spectroscopic data in the far-infrared (FIR) wavelengths. The most significant limitation for BETTII is its sensitivity; obtaining spectral signal-to-noise ratio greater than 5 in less than 10 minutes requires sources greater than 13 Janskys (Jy). One possible way to improve the signal-to-noise ratio (SNR) for future BETTII flights is by reducing the spectral bandwidth post beam-combination. This involves using a dispersive element to spread out a polychromatic point source PSF (Point Spread Function) on the detector array, such that each pixel corresponds to a small fraction of the bandwidth. This results in a broader envelope of the interferometric fringe pattern allowing more fringes to be detected, and thereby improving the spectral SNR. Here we present the analysis and optical design of the dispersive backend, discussing the tradeoffs and how it can be combined with the existing design

Optics of Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): delay lines and alignment

We present the optics of Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) as it gets ready for launch. BETTII is an 8-meter baseline far-infrared (30-90 μm) interferometer mission with capabilities of spatially resolved spectroscopy aimed at studying star formation and galaxy evolution. The instrument collects light from its two arms, makes them interfere, divides them into two science channels (30-50 μm and 60-90 μm), and focuses them onto the detectors. It also separates out the NIR light (1-2.5 μm) and uses it for tip-tilt corrections of the telescope pointing. Currently, all the optical elements have been fabricated, heat treated, coated appropriately and are mounted on their respective assemblies. We are presenting the optical design challenges for such a balloon borne spatio- spectral interferometer, and discuss how they have been mitigated. The warm and cold delay lines are an important part of this optics train. The warm delay line corrects for path length differences between the left and the right arm due to balloon pendulation, while the cold delay line is aimed at introducing a systematic path length difference, thereby generating our interferograms from where we can derive information about the spectra. The details of their design and the results of the testing of these opto-mechanical parts are also discussed. The sensitivities of different optical elements on the interferograms produced have been determined with the help of simulations using FRED software package. Accordingly, an alignment plan is drawn up which makes use of a laser tracker, a CMM, theodolites and a LUPI interferometer