Browsing by Subject "Binary stars"
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Item Advances in manufacturing and metrology of silicon immersion gratings and spectroscopy of young, low-mass stars with IGRINS(2020-08) Kidder, Benjamin Thomas; Jaffe, D. T.; Isella, Andrea; Kraus, Adam; Sneden, Christopher; Hill, GarySilicon immersion gratings will allow the Giant Magellan Telescope Near-IR Spectrograph (GMTNIRS) to achieve continuous coverage over the entire J, H, K, L and M photometric bands with resolution R~65,000, at J, H and K and R~80,000 at L and M. I describe the manufacturing process and metrology techniques for silicon immersion gratings. I overview updates to the production process and new grating metrology techniques that I have developed in order to successfully manufacture silicon immersion gratings for GMTNIRS. Most of the changes to our manufacturing process that I have contributed to, were required because of our need to produce gratings on silicon substrates larger than those we have used in the past. Gratings for J, H and K will be blazed at R3, while the L and M gratings will be blazed at R4 to achieve the desired resolution. The higher blaze angle of the L and M gratings requires that we use 150mm diameter substrates rather than the 100mm substrates that our standard process was built for. In order to accommodate the larger substrates my colleagues and I constructed a custom UV exposure system for contact printing of grating lines, and constructed fixtures for coating and etching of the larger substrates. Additionally, we implemented new process checks and metrology techniques to improve our overall grating yield for 100mm and 150mm gratings. These updates to our process have resulted in the successful production of a complete set of gratings for GMTNIRS. In addition to my work in the area of manufacturing silicon immersion gratings, I have completed two observation based projects using our existing instrument, the Immersion Grating Near-Infrared Spectrometer (IGRINS), which employs a silicon immersion grating as its primary dispersing element. The first of these projects uses IGRINS to provide updated membership information for young low-mass stars in relation to the TW Hya young moving group. Nearby young moving groups provide unique samples of similar age stars for testing the evolution of physical properties. Incomplete and/or incorrect group membership classifications reduce the usefulness of the group, which we assume to be coeval. With near-infrared spectra of two candidate members of the TW Hya Association, 2MASS J12354615-4115531 (TWA 46) and 2MASS J12371238-4021480 (TWA 47), we test their membership by adding radial velocity measurements to the literature. We find that 2MASS J12354615-4115531 is a close spectroscopic binary system with a center-of-mass radial velocity of -6.5±3.9 km s⁻¹. This radial velocity and a Gaia parallax produces a TWA membership probability of 41.9% using the Banyan ∑ tool for 2MASS J12354615-4115531. The spectrum of 2MASS J12371238-4021480 shows that it appears to be a single star with a radial velocity consistent with the TW Hya Association and a membership probability of 99.5%. The reduced probability of TWA 46 as a true member of TWA highlights the importance of high-resolution, near-infrared spectra in validating low-mass moving group members. The second astronomical observation based project in this document concerns veiling in spectra of young stars in the Taurus-Auriga star forming region. I present measurements of the H and K band veiling for 142 young stellar objects in the Taurus-Auriga star forming region using high-resolution spectra from IGRINS. In addition to providing measurements for r [subscript H] and r [subscript K] we produce low-resolution spectra of the excess emission across the H and K bands. We fit single-temperature blackbodies to the excess spectra of 42 members of our sample and measure near-IR excess temperatures ranging from 1200-2400K. We compare the luminosity of the excess continuum emission in Class II and Class III young stellar objects and find that a large number of Class III sources display a significant amount of excess flux in the near-infrared. We conclude that the mid-infrared SED slope and therefore young stellar object classification is a poor predictor of the amount of remaining inner-disk (<1AU) material. I find that 6 members of our sample contain a prominent feature in their H-band excess spectra of unknown origin that is definitively inconsistent with a single or multi-temperature blackbody.Item Kernel-phase interferometry for detection of close in companions : binary demographics of brown dwarfs from birth to maturity(2023-08) Factor, Samuel Meir; Kraus, Adam L.; Bowler, Brendan P.; Offner, Stella S. R.; Lacy, John H.; Ireland, Michael J.; Evans II, Neal J.Filling out the dearth of detections between direct imaging and radial velocity surveys will test theories of planet formation and (sub)stellar binarity across the full range of semi-major axes, connecting formation of close to wide separation gas giants and sub-stellar companions. Direct detection of close-in companions is notoriously difficult as classical techniques fail near the diffraction limit. In this dissertation, I present a new pipeline which searches for faint companions using kernel-phase interferometry (KPI), a technique utilizing interferometric analysis of the full unobscured telescope aperture. I demonstrate the pipeline, and the power of KPI, by performing two surveys and accompanying demographic analyses. First, I search for companions in the entire HST/NICMOS F110W and F170M image archive of nearby brown dwarfs (BDs), demonstrating significant sensitivity to companions at half the diffraction limit. I discover no new companions but recover and refine astrometry of 19 previous imaging companions and confirm two previous kernel-phase detections. I also present contrast curves to enable a population study and to demonstrate the strength of this technique at separations inaccessible to classical imaging techniques. Second, after estimating physical properties of a subset of this sample, I use a Bayesian framework to compare these detections and detection limits to a model companion population. When correcting for Malmquist bias, I find a smaller population of companions with tighter separations than seen in previous studies. This is due to our use of KPI, which enables us to resolve the peak of the semimajor axis distribution with significant sensitivity to low-mass companions. I confirm the previously-seen trends of decreasing binary fraction with decreasing mass and a strong preference for tight and equal-mass systems in the field-age sub-stellar regime; only ∼ 1% of systems are wider than 20 au or have a mass ratio q < 0.6. Third, I present the results of a second KPI based survey of sub-stellar objects in Taurus and Upper Scorpius using archival HST/ACS. I present 6 new candidate detections at extremely tight separations, in addition to 4 previously known companions. This is the first application of KPI to visible-wavelength observations. I find an observed companion frequency of F [subscript obs] = 0.24 [superscript +0.10][subscript −0.08] which is slightly higher than previous studies, consistent with our new detections. Combining these two surveys and demographic analyses, I find a significant excess of young wide (ρ > 10 au) companions compared to the field. I also find that the field population of wide companions is consistent with my population of systems formed in low density regions if it were to be diluted by single systems formed in high density regions. This is consistent with dynamical evolution preferentially dissolving systems born in high-density star-forming regions over those in low-density regions. I attribute the characteristics of the BD binary population to turbulent fragmentation setting the initial conditions followed by a brief period of dynamical evolution, removing the widest and lowest-mass companions, before the birth cluster dissolves.Item Spectroscopic detection and characterization of extreme flux-ratio binary systems(2016-05) Gullikson, Kevin Carl; Kraus, Adam L.; Jaffe, Daniel T; Dodson-Robinson, Sarah; Robinson, Edward L; Meyer, MichaelBinary stars and higher-order multiple systems are a ubiquitous outcome of star formation, especially as the system mass increases. The companion mass-ratio distribution is a unique probe into the conditions of the collapsing cloud core and circumstellar disk(s) of the binary fragments. Inside a ~1000 AU the disks from the two forming stars can interact, and additionally companions can form directly through disk fragmentation. We might therefore expect the mass-ratio distribution of close companions to differ from that of wide companions. This prediction is difficult to test with intermediate-mass primary stars using traditional methods because the contrast ratios that would be required to detect low-mass companions at narrow working angles are not yet achievable. In this thesis, we present a spectroscopic method to detect and characterize close companions to a variety of stars. We demonstrate applications of the method to detection of stars and even planets around sun-like stars, and present the results of a survey searching for companions to A- and B-type stars. As part of the survey, we estimate the temperatures and surface gravity of most of the 341 sample stars, and derive their masses and ages. We additionally estimate the temperatures and masses of the 64 companions we find, 23 of which are new detections. We find that the mass-ratio distribution for our sample has a turnover near q ~0.3, in contrast to the scale-free power law that describes the widely separated binary systems. We take this characteristic scale as evidence that companions are accreting a significant of material through disk interactions as they form, and that the scale is largely set by the disk lifetime and the time at which the fragments form.