To access this work you must either be on the Smith College campus OR have valid Smith login credentials.

On Campus users: To access this work if you are on campus please Select the Download button.

Off Campus users: To access this work from off campus, please select the Off-Campus button and enter your Smith username and password when prompted.

Non-Smith users: You may request this item through Interlibrary Loan at your own library.

Publication Date

2024-5

First Advisor

Kimberly Ward-Duong

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Astronomy

Keywords

Hubble Space Telescope, instrumentation, coronagraphic spectroscopy, calibration, data processing method

Abstract

Coronagraphic imaging allows us to study faint features around bright objects, and can be combined with long-slit spectroscopy by adding an occulting bar in the slit. Coronagraphic spectroscopy thus provides high contrast, spatially resolved spectra at close angular separation. Currently, the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) is the only instrument capable of performing visible light coronagraphic spectroscopy (λ ∼ 2900-10270˚A). However, this mode is rarely used and not supported by the science pipeline. We build a spectral reduction method, calibrate the performances and limitations of this mode, and create contrast curves as a function of wavelength for future reference and observation planning. The full pipeline includes basic reduction, defringing, centering, point spread function (PSF) subtraction, noise estimation, and spectral extraction. We test the pipeline on archival observations of GJ 784, which was used as a PSF reference star for the debris disc host AU Mic. These observations were taken in the G750L mode (a low-resolution spectrum (R ∼ 500) covering wavelengths between 5200∼10270˚A). Two epochs of observations were taken in 2012 and 2021, and classical reference differential imaging (RDI) on these two datasets established a baseline scenario for PSF subtraction. We use the standard deviation of noise as a metric of contrast at various wavelengths and separations. Our estimation suggests the 1α contrast at 1” is on the order of 10−5 ∼ 10−6. Our dedicated calibration program (Proposal ID: 17902) explores the possibility of using coronagraphic spectroscopy on close separation systems. We discuss the impact on contrast estimation when a central star is placed at non-default locations behind the occulting bar. The non-default locations allow us to place the center object closer to the edge of the bar to study companions and environments at extremely close (200 mas) separation. The calibration program also observed a white dwarf companion, HD 114174B, with an easily modeled spectrum. We use this observation and an unknown brown dwarf that falls into the slit in the previous close separation observation to validate our contrast estimation.

Rights

©2024 Jingyi Zhang. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

Comments

v, 93 pages: color illustrations, charts. Includes bibliographical references (pages 89-93).

Download

Smith Only:
Off Campus Download

Share

COinS