Detection of the emission from the secondary component in a binary system can be extremely challenging, but equally rewarding. In the case of intermediate to high-mass binaries, detection of close companions can inform formation theories. In the extreme low mass-ratio case, where the secondary component is in fact a planet, detection of the emission in high resolution spectroscopy can be used to determine the true planet mass. In this thesis, we describe a technique to detect the thermal emission from the secondary component of a low mass-ratio binary system. We apply this technique to archived observations of early B-type stars using VLT/CRIRES, and simulate future observations of planetary systems with IGRINS, a near-infrared spectrograph being built now. / text

A wide range of observed luminosities of young forming stars conflicts with predictions of the standard star formation model, which features a constant accretion rate. To resolve this discrepancy, an episodic accretion model has been suggested. The focus of this dissertation is to test this model in low mass star formation. I present new observations of the CB130 region. The observed photometric data from Spitzer and ground-based telescopes are used to determine the luminosity, and radiative transfer modeling of dust and gas are used to characterize the envelope and disk. I compare molecular line observations to models to constrain the chemical characteristics and abundance variations. Based on the chemical model result and molecular line observations, the low luminosity of the embedded protostar is explained better as a quiescent stage between episodic accretion bursts rather than as the first hydrostatic core stage. I present CO₂ ice observations toward 19 low luminosity embedded protostars. About half of the sources have evidence for pure CO₂ ice, and six have significant double-peaked features, which are strong evidence of pure CO₂ ice. The presence of detectable amounts of pure CO₂ ice signify a higher past luminosity, consistent with the past high accretion. Using chemical evolution modeling, the episodic accretion scenario, in which mixed CO-CO₂ ice is converted to pure CO₂ ice during each high luminosity phase, explains the presence of pure CO₂ ice, the total amount of CO₂ ice, and the observed residual C18O gas. I used CARMA to observe a sample of embedded protostars that spans the full range of protostellar luminosities, especially lower luminosity sources. The standard model predicts the disk mass increases steadily while the episodic accretion model predicts no clear relationship between disk mass and bolometric temperature. Masses of six detected disks spread out regardless of bolometric temperature. With the pure CO₂ ice detection, I can explain disk masses of the source in the context of episodic mass accretion. I conclude that episodic mass accretion provides a good explanation of the low luminosity of protostars, molecular line strength, pure CO₂ ice detection, total CO₂ ice amount and spread of disk masses. / text

This thesis presents the results of a survey of 913 M-dwarf stars from the Lepine and Shara Proper Motion (LSPM) catalog within 33 parsecs. Data for these targets was collected with the Robo-AO camera on the Palomar 60” telescope. In order to determine which stars were in bound systems, the images with multiple stars, first observed in 2012, were observed again in 2014 to examine changes in separation and position angles. Stars with little change in position with respect to one another suggest they are common proper motion pairs. The Washington Double Star (WDS) catalog and other resources were used to further determine binarity. This research was conducted to improve upon the statistics of nearby multiple M-dwarf systems. Identifying and confirming multiple systems at both wide and small separations will improve our understanding of M-dwarf formation by comparing these results to existing star formation models.

High resolution observations have been made of a number of southern Cepheids to make an observational and theoretical study of Cepheid variables using radial velocities. The stars studied were part of a long term programme to observe southern variable stars, from which a valuable database of radial velocities gathered over a long period were available. Sixteen échelle spectrograph orders in the wavelength region 5400 - 8600Å were used, which included a number of absorption lines covering a range of species and excitation potentials. The line bisector technique was used to measure stellar and telluric lines and to obtain radial velocities. To improve the precision of the radial velocities we used telluric lines to calibrate the observations to a common reference frame. The radial velocities have a precision of ~300ms⁻¹ allowing the detection of velocity differences of ~1 kms⁻¹ with confidence. The radial velocity data obtained at Mount John University Observatory (MJUO) was combined with data from various sources to determine the orbits of any Cepheids exhibiting orbital motion. The various orbital parameters were determined for a number of systems and where radial velocities for the companions exist, some estimate of the mass was made. The precision of the radial velocities obtained from MJUO also allowed us to search for line level effects for a number of species among the Cepheid spectra. A number of IAU standard stars were observed to calibrate the radial velocities obtained at MJUO to the IAU standard scale. The radial velocities from MJUO were found not to differ significantly from the IAU values. Binary Cepheids are particularly useful in the determination of Cepheid masses, which are still an active topic for astronomical research. The value of the MJUO data was that it provided a consistent set of data against which other sources of data could be compared. For 8 of the Cepheids new or improved orbital solutions were found. They are Y Car, YZ Car, AX Cir, BP Cir, S Mus, V636 Sco, V350 Sgr, W Sgr and T Mon. Of these 8 systems, 3 had radial velocities for their respective companions which allowed the determination of the mass of the Cepheids. Masses were determined for the 9 day Cepheid S Mus (6.0±0.4M⊙), the double mode Cepheid Y Car (4.5±1.8 M⊙) and the 5 day Cepheid V350 Sgr (6.0±0.9 M⊙). New results presented here include the first orbital solution for the binary Cepheid AX Cir, a completely revised orbital solution for the binary Cepheid YZ Car which established its eccentricity, and orbital motion. The binary Cepheid BP Cir however was found to require a new pulsation period of 2.39819d to fit the observed pulsational velocities. Observations of the suspected binary Y Oph show it to be an unusual Cepheid with no evidence of binarity (~0.5 kms⁻¹) in our data. Finally, the 5 day Cepheid W Sgr was observed to have the lowest orbital amplitude measured. We discussed the line level effects found in our observations, where a number of spectral lines were observed to show departures from the Fei velocity curve. Line level effects were observed in H⍺, CaⅡ, BaⅡ, FeⅡ, SiⅠ and SiⅡ. Most of the Cepheids were observed to show the same progression of line level effects, with the best example being the bright Cepheid β Dor. The SiⅡ velocities indicate that these lines have the lowest velocity amplitude and form deeper in the atmosphere than the FeⅠ, where as the CaⅡ and H⍺ lines were all observed to have much greater velocity amplitudes with the peak of these velocity curves occurring later, in pulsational phase. These observations are consistent with the lines forming at different depths as a density wave propagates through the atmosphere. X Sgr is peculiar due to its interesting spectra which at certain phases show line doubling and at most other phases the lines were asymmetric. These observations are interpreted to support the idea that X Sgr has strong shock waves present and that X Sgr has greater atmospheric transparency in the spectral region near 6000Å. We also present the results of dynamical modelling of a pulsating Cepheid. Using a non-linear radiative hydrodynamic code developed by A. Fokin, we have modelled two Cepheids, AX Cir and YZ Car. These models have then been compared with the observations obtained here. After extensive modelling using the latest OP opacities, it has been determined that the Cepheid AX Cir can be modelled using parameters L = 2050 L⊙, M = 4.8 M⊙ and Teff = 5900K. The model reproduced the observed stellar characteristics, such as the photometric amplitude and pulsational period. Comparison between the observations and the model for the selected spectral lines, FeⅠ 5576Å, SiⅡ 6347Å, BaⅡ 5853Å and CaⅡ 8542Å show good agreement with similar amplitudes and velocity curves. With no strong shock waves being produced by the model, the observed line level effects can be explained by a density wave. The 18 day Cepheid YZ Car was chosen to explore the capabilities of the radiative hydrodynamic code for a long period Cepheid. The best model developed that reproduced the observed stellar characteristics had parameters L = 9350 L⊙, M = 7.7 M⊙ and Teff = 5590K. The period was 18.314 days and the bolometric light curve agreed well with the observed visual light curve. Comparison of the theoretical and observed radial velocities showed good agreement.

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No description available.

No description available.

Observations and analysis of globular cluster systems associated with three galaxy types are presented. Spectroscopy of globular cluster (GC) candidates in the Sculptor spirals NGC 253 and NGC 55 has identified 15 GCs in these galaxies. This spectroscopic sample, combined with plate scans, indicates total GC populations consistent with that expected for their luminosity and morphological type. From these data, we define new GC samples for spectroscopy. Radial velocities of 87 GCs in the Virgo elliptical NGC 4472 have been obtained, yielding data for 144 GCs when combined with previous studies. We find the blue GCs have significantly higher velocity dispersion than the red GCs, with little rotation in either population. The GCs dispersion profile declines slowly, yielding mass profiles consistent with X-ray data. We find a steeply rising M/L ratio, indicative of a massive dark halo surrounding this galaxy. From line-strengths of the GCs, we derive ages and metallicities for the GCs using simple stellar population (SSP) models. We find that the GCs are old and coeval and the bimodality seen in then- colours reflects metallicity rather than age differences. The GCs exhibit solar abundance ratios and both subpopulations show evidence for radial metallicity gradients. We have obtained high S/N spectra for 64 star clusters in the Large Magellanic Cloud. We measure their Lick indices to test the age and metallicity calibration of SSP models by comparison with literature values. We find our metallicities are consistent, although the values from our integrated spectra are slightly higher. The agreement of the ages for the old GCs is good, but is somewhat poorer for the youngest clusters. We obtain an age-metallicity relation for the clusters consistent with the galaxy's field stars. We show first results of a project to investigate the age and metallicity distributions of globular cluster systems using semi-analytic models of galaxy formation.

Solid hydrogen coated graphite particles may be expelled from regions of star -formation into the general interstellar medium. The solid para- hydrogen mantles, which contain a small proportion of orthomolecules are stable against evaporation in the general interstellar radiation field. They are also stable against physical and chemical sputtering in HI regions. Extinction efficiencies are calculated for solid hydrogen particles and for graphite particles with solid hydrogen mantles. Graphite core -solid hydrogen grains are capable of producing excellent agreement with the interstellar extinction observations from 2u - 1100 A. The graphite core radius may be in the range ro = 0.04 - 0.06u and the solid hydrogen mantle radius in the range r = 0.15 - 0.25u. The albedo and phase function of these particles are consistent with the requirements imposed by the diffuse galactic light. Solid hydrogen is strongly anisotropic in its crystal structure and optical properties. Approximate models yield good agreement with the observed trends of the wavelength dependence of interstellar polarisation.

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