Past Research of Dr. Donald Luttermoser

This page gives details of the research that I have done during my time as an undergraduate student (at University of Michigan - Ann Arbor), a graduate student (at Indiana University), and as a professional astronomer (at JILA, Iowa State University, NASA/Goddard, and ETSU).

Undergraduate Research (1980 - 1981):

Modeling Quasi-Static Solar Coronal Loops with Nonuniform Energy Input:

This work was carried out in the fall of 1980 for my undergraduate thesis under the direction of Dr. Richard Teske of the Department of Astronomy at the University of Michigan in Ann Arbor. I created a code to model solar coronal loops under the assuption of hydrostatic equilibrium by solving a set of 3 ordinary differential equations describing the temperature gradient, the electron density gradient, and the conductive flux gradient. Details of this work can be found in Luttermoser (1981).

Graduate Research (1983 - 1988):

Hydrogen-Deficient Atmospheres for Cool Carbon Stars:

This work was carried out in the spring of 1984 as part of a course project for the graduate-level course Stellar Atmospheres (A540) taught by Dr. Hollis Johnson. The class converged models atmospheres representative of cool (N-type) carbon stars for decreasingly amounts of hydrogen starting from solar abundance. Motivated by recent work which hints at a possible deficiency of hydrogen in non-Mira N-type carbon stars and to further explore the parameter space of chemical composition, computations were made of a series of hydrogen-deficient models for carbon stars. For these models Teff = 3000 K, and log g = 0.0. Solar abundances are used for all elements except for carbon (which is enhanced to give C/O = 1.05), hydrogen, and helium. As the fractional abundance of hydrogen is decreased, being replaced by helium, the temperature-optical depth relation is affected only slightly, but the temperature-pressure relation is changed. The most striking change in the emergent flux is the decrease of the H^- peak at 1.65 micron compared with the blackbody peak at 1.00 micron. Results of this work can be found in the Astrophysical Journal (ApJ) paper Johnson et.al. (1985).

Full Disk Continuum Photometry with the NSO/Tusson Vacuum Telescope:

This work was carried out in the summer of 1984 at the NSO/Tucson Solar Vacuum Telescope on Kitt Peak while on a NSF/NASA Graduate Summer Research Assistantship under the direction of Dr. Harry Jones. For this work, photoelectric scans with a 0.25-Angstrom bandpass of the solar disk were made in a clean continuum region at 5256.3-Angstroms throughout that summer. Software was developed to reduce this data in order to see if small variations in the solar irradiance could be dedected from the ground as active regions crossed the solar disk. Results of this work was presented at the Solar Physics Division of the American Astronomical Society (AAS) meeting during the summer of 1985. An abstract of this poster can be found at Luttermoser & Jones (1985).

Ultraviolet Spectra and Chromospheres of Cool Carbon Stars:

This work was carried out as part of my research for my Ph.D. dissertation. I have a variety of conference proceedings and professional meeting poster abstracts associated with this work (see my CV for a complete list). This work also was published in the ApJ article Johnson & Luttermoser (1987), which corresponds to Chapter 2 of my dissertation. The authors assembled and discussed all available low-resolution IUE spectra of N-type carbon stars -- including TW Hor, BL Ori, UU Aur, NP Pup, U Hya, T Ind, and TX Psc. Identification of spectral features is aided by a composite spectrum. Shortward of 2850 A only emission lines of C II, Mg II, Al II, and Fe II are seen, while the spectrum longward of 2850 A appears to be a photospheric absorption spectrum with a few superposed emission lines of Fe II. The most prominent absorption features are due to Fe I, CH, and CaCl. The emission feature at 2325 A, second only to Mg II in strength, is conclusively identified as C II (UV 0.01). Ultraviolet spectra of N-type carbon stars are similar to, though the emission-line fluxes are generally weaker than, those of the coolest M-giant stars available, such as HD 18191 (M6 III).

The Violet and Ultraviolet Opacity Problem for Carbon Stars:

This work was carried out as part of my research for my Ph.D. dissertation. The work was published in the ApJ article Johnson, Luttermoser, & Faulkner (1988), which corresponds to Chapter 3 of my dissertation. This paper considers the longstanding problem of the 'violet opacity' in cool carbon stars by testing, through synthetic spectra, many new and previously suggested opacity sources, based on currently available model atmospheres for carbon stars and M giant stars at that time. While several bound-free edges of neutral metals are important opacity sources, those of Na I at at 2413 A, Mg I at 2514 A, and particularly Ca I at 2940 A are especially significant. Collectively, thousands of atomic lines are important, and the enormous line of Mg I at 2852 A influences the spectrum well into the visible. The pseudocontinuum of C3 and the photoionization continuum of CH both play noticeable but secondary roles. Synthetic spectra form the carbon star models with and without polyatomic molecules fit nicely the collected observations of the well-observed carbon star TX Psc.

The Chromospheric Structure of Cool Carbon Stars:

This work was carried out as part of my research for my Ph.D. dissertation. I have a variety of conference proceedings and professional meeting poster abstracts associated with this work (see my CV for a complete list). This work also was published in the ApJ article Luttermoser, Johnson, Avrett, & Loeser (1989), which corresponds to Chapter 4 of my dissertation. In this work, a semiempirical chromospheric model is proposed for TX Psc which is a prototype for the N-type carbon stars. Observational data imply that the chromospheric temperature rise must begin at a low density, that the temperature gradient in the lower chromosphere must be steep, that partial redistribution must be employed in the Mg II calculation, and that the lower chromosphere is expanding away from the photosphere with a velocity of close to 50 km/s. The present model also shows that the microturbulent velocity is about 7 km/s at the temperature minimum region, dropping to 5 km/s in the chromosphere, and that the Lyman lines are optically thick in the chromosphere.

Postdoc Research at JILA (1988 - 1990):

Ionization and Excitation in Cool Giant Stars:

This work was carried out as part of my research for my Ph.D. dissertation and continued during my first dostdoc at the Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado. I have a variety of conference proceedings and professional meeting poster abstracts associated with this work (see my CV for a complete list). This work also was published in the ApJ article Luttermoser & Johnson (1992), which partially corresponds to Chapter 5 of my dissertation. For this work, the influence that non-LTE radiative transfer has on the electron density, ionization equilibrium, and excitation equilibrium in model atmospheres representative of both oxygen-rich and carbon-rich red giant stars was demonstrated. The radiative transfer and statistical equilibrium equations were solved self-consistently for H, H^-, H₂, He I, C I, C II, Na I, Mg I, Mg II, Ca I, and Ca II in a plane-parallel static medium. Calculations were made for both radiative-equilibrium model photospheres alone and model photospheres with attached chromospheric models as determined semiempirically with IUE spectra of g Her (M6 III) and TX Psc (C6, 2). The excitation and ionization results for hydrogen and helium are reported in the above mentioned ApJ paper.

A New Collaboration to Model the Atmospheres of Mira-Variable Stars:

This collaboration was initially set up during my first dostdoc at the Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado. For this collaboration, Dr. George Bowen and Dr. Lee Anne Willson of Iowa State University and myself worked to combine hydrodynamic modeling with NLTE radiative transfer calculations to model the Mira variable stars -- see Luttermoser, et.al. (1988) for the announcement of this collaboration. For this work, the Iowa State group supplied hydrodynamic models representative of Mira-type variables to me in order to carry out the radiative transfer. I used the PANDORA code to solve the NLTE radiative transfer in these models to generate synthetic spectra for comparison with spectral observations made of these stars, and to generate a table of radiative heating and cooling rates to be used in subsequent hydrodynamic calculations. Early results of this work was published in the "6th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun" conference proceedings article Luttermoser & Bowen (1990).

The Formation of He I Lambda-10830 in Cool Giant Stars:

This work was carried out during my first dostdoc at the Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado. In this work, I used Dr. Manfred Cuntz's hydrodynamic models of red giant stars to calculate non-local thermodynamic equilibrium (NLTE) synthetic spectra of the He I (neutral helium) transition at 10,830-Angstroms in order to determine whether stochastic shock waves could excite this transition in noncoronal giant stars. This work was published in the ApJ article Cuntz & Luttermoser (1990). The question of whether strong shocks produced in time-dependent stochastic wave models can explain the formation of the He I 10830-A line in cool giant stars was examined. The research is based on the ab initio chromosphere model for Arcturus by Cuntz (1987), showing that a stochastic distribution of wave periods leads to overtaking and merging of shocks, which occasionally produce very strong shocks with temperatures larger than 40,000 K in the postshock regions. These temperatures can easily produce a significant population in the 2s ³S state by electron collisional excitation. The 10830-A line occurs in absorption when the densities in the shocks exceed 10 million/cm³.

Astronomy at FUV and EUV Wavelengths:

This work was carried out during my first dostdoc at the Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado. In anticipation of more sensitive EUV and FUV spectroscopic instruments, Dr. Jeff Linsky and I simulated spectra, including interstellar absorption, of solar-like, RS CVn, and flare stars as folded through the instrument parameters of the EUVE, Lyman/FUSE Phase A, and a desirable next-generation spectrometer. We found that even the relatively insensitive EUVE spectrometer will be able to detect sufficient spectral lines from many active binary and dMe stars to determine their coronal emission measure distributions. The Lyman/FUSE or next-generation spectrometers are needed to study solar-type stars or flaring stars with high time resolution. The high throughput and effective area of a next-generation spectrometer is needed for Doppler imaging studies, stellar wind and downflow measurements, and high time and spectral resolution of stellar flares. This work was published in the Advances in Space Research Conference Proceedings article Linsky & Luttermoser (1991).

A VLA Survey of N-type Carbon Stars:

This work was carried out during my first dostdoc at the Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado. In this work, Dr. Alex Brown and I undertook a survey of N-type carbon stars at radio wavelengths with the Very Large Array (VLA) in New Mexico to see if these stars had any radio emission from their chromospheres. Although most of the stars in our sample displayed no radio emission, the peculiar carbon star V Hya was detected. This work was published in the ApJ article Luttermoser & Brown (1992). Specifically, the results were presented of a VLA-continuum survey of 7 N-type carbon stars at 3.6 cm. Evidence exists for hot plasma around such stars; the IUE satellite detected emission lines of singly ionized metals in the optically brightest carbon stars, which in solar-type stars indicate the existence of a chromosphere. In the past, these emission lines were used to constrain the lower portion of the archetypical chromospheric model of N-type carbon stars, that of TX Psc. Five of the survey stars are semiregular (1 SRa and 4 SRb) variables and two are irregular (Lb) variables. Upper limits of about 0.07 mJy are set of the SRb and Lb variables and the lone SRa (V Hya) was detected with a flux of 0.22 mJy. The upper limits for the six stars that are not detected indicate that the temperature in their winds is less than 10,000 K. Various scenarios for the emission from V Hya are proposed, and it is suggested that the radio continuum is shock-related (either due to pulsation or the suspected bipolar jet) and not due to a supposed accretion disk around an unseen companion.

Emission Line Profile Variations in M-giants:

This work was carried out during my first dostdoc at the Joint Institute for Laboratory Astrophysics (JILA) at the University of Colorado. I worked with Dr. Phil Judge, Dr. Bob Stencel, Dr. Manfred Cuntz and Don Neff on this project. A time-series analysis was performed using high dispersion spectra of the Mg II, k, Ca II H, and K lines of the semiregular giants Rho Per (M4 II-III, periodicity of about 50 days), R Lyr (M5 III, period of about 46 days), and g Her (M6 III, period of about 90 days). The fine error sensor on the IUE satellite and ground based UBV photometry was used to relate line profile variations to photospheric variations. The above mentioned stars were selected to study the relative importance of convective motions and global stellar pulsations in determining the structure of the outer atmospheres. Small amplitude changes, but substantial changes in the profiles of Mg II and Ca II lines were detected. It is contended that the observed variability is due to changes in chromospheric conditions and not variations within the circumstellar shell. The picture of a steady state chromosphere, which is modulated on long time scales, was corroborated by these observations. In addition, localized heating was found in g Her. Results of this work can be found in the Astronomical Journal (AJ) article Judge, Luttermoser, Neff, Cuntz, & Stencel (1993).

My Research at Iowa State University (1990 - 1993):

Fluorescent Clues to the Atmospheric Structure of AGB Stars:

This work was started during my JILA years and continued during my years at Iowa State University and NASA/Goddard. For this work, I carried out near-coincident observations of oxygen-rich and carbon-rich, semiregular and Mira-type variable asymptotic giant branch (AGB) stars using both the ground-based McMath-Pierce Telescope on Kitt Peak, AZ using its stellar spectrograph and the International Ultraviolet Explorer (IUE) spacecraft operated by NASA/Goddard and the European Space Agency (ESA). These observations were made to investigate the differences between the atmospheric structure of Mira-type and semiregular variables through the Fe I (42) lines at 4202 Angstroms and 4308 Angstroms. These lines are fluoresced by the Mg II lines near 2800 Angstroms via an Fe I (UV3) transition. The Fe I (42) lines peak in flux at the same phase (~0.3) as the Mg II lines in the Mira stars, which corresponds to a ~0.3 phase lag behind the peak Balmer line flux. NLTE radiative transfer calculations show that this phase lag between the Mg II and the Balmer line peak fluxes results from the existence of a permanent chromosphere (or calorisphere) in the Mira. The fact that Fe I (42) variability matches the Mg II variability indicates that these fluorescent lines originate from a cooler circumstellar shell and not from the inner-shock region or photosphere. The Fe I (42) lines in the semiregular variables do not vary from changes in the Mg II flux. This suggests that the circumstellar shells surrounding semiregulars are not as optically thick as those around Miras. Result of this work can be found in Luttermoser (1996).

Inhomogenious Atmospheres for Non-Mira Red Giant Stars:

This work was carried during my years at Iowa State University in collaboration with Dr. Hollis Johnson (my Ph.D. dissertation advisor) and Dr. Uffe Jorgensen. Here we carried out NLTE calculations for semiempirical chromospheric models and radiative equilibrium photospheric models to try and ascertain whether non-Mira red giant stellar atmospheres are inhomogeneous. Result of this work did suggest this is the case (see Johnson, Jorgensen, & Luttermoser 1991).

NLTE Synthetic Spectra of Mira-type Variable Stars:

This work was started during my JILA years and continued during my years at Iowa State University and beyond. I have a variety of conference proceedings and professional meeting poster abstracts associated with this work (see my CV for a complete list). The following papers give a highlight of this work: Luttermoser & Bowen (1992), Luttermoser (1992), and Luttermoser, Bowen, & Willson (1993). A useful summary of this work can be found at Luttermoser (2009a). Prior to 2008, I have been focusing on ultraviolet, visual, and near-infrared spectra. However in the recent past, I have expanded my wavelength coverage to include mid- and far-infrared spectra using observations obtained with Spitzer (see below).

The Chromospheric Structure of the Cool Giant g Herculis:

This work was carried during my years at Indiana University, JILA, and Iowa State University. Here a semiempirical chromospheric model was determined for the semiregular red giant star g Her (M6 III) following the same techniques to model the chromosphere of the carbon star TX Psc. Results of this work ican be found in Luttermoser, Johnson, & Eaton (1994). For this work, non-Local Thermodynamic Equilibrium (NLTE) calculations of semiempirical chromospheric models were presented for 30 g Her (M6 III). This star is one of the coolest (Teff = 3250 K) SRb (semiregular) variable stars and has a mass perhaps as great as 4 solar masses. Chromospheric features were observed in its spectrum including Mg II h and k; C II] UV0.01, which is sensitive to electron density; Mg I lambda 2852; Ca II H, K, and IRT; Ca I lambda 4227 and lambda 6573; Al II] UV 1; and H alpha. Special attention was paid to fitting the C II intersystem lines and the Mg II resonance lines but used all the other features as constraints to some extent. The equations of radiative transfer and statistical equilibrium were solved self-consistently for H I, H^-, H₂, He I, C I, C II, Na I, Mg I, Mg II, Al I, Al II, Ca I, and Ca II with the equivalent two-level technique. To simplify these calculations, a one-dimensional hydrostatic, plane-parallel atmosphere was assumed. The investigation used 10 separate 'classical' chromospheric models, differing most importantly in total mass column density above the temperature minimum. Synthetic spectra from these models fit some but not all of the observations. These comparisons were discussed in detail. However, it was found that no single-component classical model in hydrostatic equilibrium is able to reproduce both the Mg II line profiles and the relative strengths of the CII] lines. In all these models, chromospheric emission features are formed relatively close to the star (approximately less than 0.05 R_*). The circumstellar environment has a thick, cool component overlying the Mg II emission region, which is relatively static and very turbulent. Finally, it was found that thermalization in the Mg II h and k lines in the coolest giant stars is controlled by continuum absorption from Ca I 4p 4p³ P_o bound-free opacity and not collisional de-excitation as is the case for warmer K giants.

Effect of Chromospheric and Shock Photons on Molecular and Atomic Opacities:

This work was carried during my years at Iowa State University. The various NLTE radiative transfer calculations for which I have been involved while modeling semiempirical chromospheric models and dynamic Mira-type models have shown that the UV photons from the emission lines at these wavelength have a significant impact on the formation, level excitation equilibrium and ionization equilibrium in these stars. A summary of this work is given in Luttermoser, et.al. (1993).

My Research at NASA/Goddard (1993 - 1996):

HST Observations of the Chromosphere of a Carbon Star:

This work was started during my Iowa State University years and continued during my years at the NASA Goddard Space Flight Center. This work was carried out with a large group of scientists lead by Dr. Hollis Johnson and Dr. Lisa Ensman in order to advance our understanding of the relationship between stellar chromospheres and mass loss, which is a common property of carbon stars and other asymptotic giant branch stars. We obtained ultraviolet spectra of the nearby N-type carbon star UU Aur using the Hubble Space Telescope (HST). In Johnson, et.al. (1995) we described the HST observations, identify spectral features in both absorption and emission, and attempt to infer the velocity field in the chromosphere, upper troposphere, and circumstellar envelope from spectral line shifts. A mechanism for producing fluoresced emission to explain a previously unobserved emission line also was proposed. In addition, related ground-based observations also were described.

The Chromosphere/Shock Dilemma of Non-Mira, Late-Type Variable Stars:

This work was carried out during my NASA/Goddard years while working for the now defunct Applied Research Corporation. Here I investigate the similarity and differences between the atmospheric structure of Mira-type and semiregular variable red giant stars through an analysis of previously obtained IUE data and NLTE radiative transfer calculations of hydrodynamic models representative of these stars. Miras are known to have global shock waves that propagate outward through the outer atmosphere as the star pulsates (which may be responsible for the UV emission lines that are seen), whereas semiregular variables have always been modeled with a classical hydrostatic chromosphere in order to reproduce the UV emission lines seen in the spectra of these stars. This research wanted to answer the question: Are global shock waves also present in the semiregular variables similar to that in the Mira variables? Both types of variables have similar effective temperatures and surface gravities, so why should their atmospheric structures be so dissimilar? The results of this work clearly indicate that the outer atmospheres of both Mira and semiregular variables are related in that both contain a chromospheric-type layer of enhanced temperature above the continuum formation depths and outward moving shocks (which produce this chromosphere). The only difference is the strength of the shocks -- the shocks in the semiregular variables are not nearly as strong (T_sh < 8000 K) as they are in the Miras (T_sh > 8000 K). Further results can be found in Luttermoser (1996) and Luttermoser (2000).

My Research at ETSU (1996 - present):

Spectroscopy of Mira Variables at Different Phases:

This work was carried out in collaboration with Dr. Mike Castelaz. Spectroscopic measurements of Mira variable stars, as a function of phase, probe the stellar atmospheres and underlying pulsation mechanisms. Modeling the atmospheres is difficult due to the hydrodynamic nature of the gas as deduced from the large light variations and velocity measurements of various spectral lines. Many questions still need to be resolved concerning the atmospheres of these stars. Are the depths of formation of the molecular species such as TiO, VO, and ZrO produced in an extended region above the layers where Balmer line emission occurs or below this shocked region? What is the explanation for the Balmer-line increment, where the strongest Balmer line at phase zero is H-delta and not H-alpha? Furthermore, why is the H-epsilon line virtually absent in the spectra of Miras when the other Balmer lines are strong? A new program of low resolution (1.08 Å/pixel) spectroscopy from about 6000 Å to 8750 Å is presented in this paper. The spectra are taken in a region which includes H-alpha, TiO, VO, ZrO, and the Ca II infrared (IR) triplet. Spectra of nine Mira variables are presented. Seven Mira variable stars (omega Cet [Mira], U Ori, R Leo, V CVn, R CVn, V Boo, and chi Cyg) were observed at more than one phase. Two other Mira variables (R Tri and R Gem) were observed at a single phase, but both show strong H-alpha emission. In this paper, we investigate the final question listed above by noting variations in the Ca II IR triplet in relationship with H-alpha variations as a function of phase. These preliminary observations suggest that H-epsilon's observational characteristics result from an interaction of H-epsilon photons with the Ca II H line. This work was published in Castelaz & Luttermoser (1997).

Effective Temperature and Surface Gravity of Mira Variables:

I supervised the work Summer 1998 REU student Robert Piontek as a faculty member at East Tennessee State University (ETSU). Synthetic and observed spectra were compared to yield effective temperatures and surface gravities for three Mira variables, R Leo, V CVn, and R CVn as a function of phase. Spectra are synthesized with ATLAS, using model atmospheres obtained from the Kurucz and Indiana University datasets. Experimental data was provided by M.W. Castelaz and E. Messer, and a best fit was determined between the two. Zirconium oxide at 6500 Angstroms was found to be a good indicator of surface gravity. We found a general decrease in Teff and log g as phase increases from 0 to 0.5, which is consistent with observed visual magnitudes. This work was presented at the 194th meeting of the American Astronomical Society (see Piontek & Luttermoser 1999).

The Atmosphere of Mira Variables: A View with the Hubble Space Telescope (GHRS Spectra):

Ultraviolet spectra was obtained with Hubble Space Telescope (HST) of two Mira-type variable stars, R Leo and R Hya, are presented, along with analysis providing information on their outer atmospheres. These high-dispersion spectra were taken with the Goddard High Resolution Spectrograph (HRS) in two spectral regions: 2320-2368 Å to record the C II] (UV0.01) multiplet and 2785-2835 Å to obtain the Mg II h and k lines. The R Hya spectrum was obtained at visual light phase 0.26 and shows a Mg II spectrum that is very clean, showing clear evidence for the overlying circumstellar absorption from Fe I (UV3) and Mn I (UV1) over the k line. The fluoresced Fe I (UV44) feature at 2824 Å is plainly visible in this spectrum, whereas past International Ultraviolet Explorer (IUE) observations of Mira variables at high dispersion were unable to record this feature. Remarkably, the newly identified fluoresced Fe I (UV45) feature near 2807 Å is seen in this spectrum. Until now, this line has been seen only in cool carbon stars with HST/HRS. This line is pumped by the thin C II] (UV0.01) emission line at 2325.5 Å. Two of the strongest C II] (UV0.01) lines near 2325 Å are plainly seen in this spectrum. This region of the spectrum, however, is dominated by the Si II] (UV0.01) line near 2335 Å, in contrast to that observed in the carbon stars and the non-Mira oxygen-rich red giant stars. Very weak Mg II lines are seen in the R Leo spectrum at phase 0.12. At this phase, these lines are typically absent in IUE spectra. Velocity shifts of emission features in the UV spectra of Mira variables are consistent with previously published hydrodynamic models of these stars. These velocities indicate, however, that the C II] (UV0.01) emission lines are not formed in the same atmospheric layers as the Mg II emission. The electron density deduced from the C II] (UV0.01) multiplet is ~10⁹ cm^-3. Finally, the temperature-density structure of the semiregular variable carbon stars is similar to the oxygen-rich Mira variables -- both are hydrodynamic in nature; however, the carbon stars macroscopic velocity fields are not identical to the Mira stars in the atmosphere layers between the Mg II emission region and the circumstellar shell. This work was published in Luttermoser (2000).

Phase-Dependent Spectroscopy of Mira Variable Stars:

This work was carried out in collaboration with Dr. Mike Castelaz, Dr. Dan Caton, and Mr. Rob Piontek. Spectroscopic measurements of Mira variable stars as a function of phase probe the stellar atmospheres and underlying pulsation mechanisms. For example, measuring variations in TiO, VO, and ZrO with phase can be used to help determine whether these molecular species are produced in an extended region above the layers where Balmer line emission occurs or below this shocked region. Using the same methods, the Balmer line increment, where the strongest Balmer line at phase zero is H-delta and not H-alpha, can be measured and explanations tested, along with another peculiarity, the absence of the H-epsilon line in the spectra of Mira variables when the other Balmer lines are strong. We present new spectra covering the spectral range from 6200 to 9000 Å of 20 Mira variables. A relationship between variations in the Ca II IR triplet and H-alpha as a function of phase support the hypothesis that H-epsilon's observational characteristics result from an interaction of H-epsilon photons with the Ca II H line. New periods and epochs of variability are also presented for each star. This work was published in Castelaz, Luttermoser, Caton, & Piontek (2000).

Vanadium Oxide in the Spectra of Mira Variables:

This work was carried out in collaboration with Dr. Mike Castelaz and Mr. Rob Piontek. As a preliminary step in deducing Teff and log g of Mira variables as a function of phase, a comparison was made between spectra synthesized from LTE stellar atmosphere models and observed spectra. The observed spectra show obvious vanadium oxide (VO) absorption bands. However, the molecular line list used to produce the synthetic spectra did not include the bound-bound VO opacities. The wavenumbers, line oscillator strengths, and lowest energy levels are needed to calculate these opacities. The equations, constants, and experimentally determined factors required to calculate the line oscillator strengths and lowest energy levels from experimentally determined wavenumbers were presented. The effect of including the wavenumbers, line oscillator strengths, and lowest energy levels of the VO B-X (0, 0) band were calculated and showed the expected absorption features observed in the spectra of Mira variables. In the VO B-X (0, 0) band the line oscillator strengths ranged from about 0.05 to 3. Results of this work was published in Castelaz, Luttermoser & Piontek (2000).

Infrared Light Curves of Mira Variable Stars from COBE DIRBE Data:

Dr. Beverly Smith, Dr. David Leisawitz, Dr. Mike Castelaz and myself used the COBE DIRBE database to derive near- and mid-infrared light curves for a well-defined sample of 38 infrared-bright Mira variable stars and compared with optical data from the AAVSO. In general the 3.5 and 4.9 micron DIRBE bandpasses provide the light curves with the best signal-to-noise ratio (S/N), with S/N decreasing with wavelength at longer wavelengths. At 25 microns good light curves are only available for ~10% of the stars in the sample, and at wavelengths >=60 microns extracting high quality light curves is not possible. The amplitude of variability was typically less in the near-infrared than in the optical and less in the mid-infrared than in the near-infrared, with decreasing amplitude with increasing wavelength. On average there were 0.20+/-0.01 mag variation at 1.25 microns and 0.14+/-0.01 mag variation at 4.9 microns for each magnitude variation in V. The observed amplitudes were consistent with results of recent theoretical models of circumstellar dust shells around Mira variables. For a few stars in our sample we find clear evidence of time lags between the optical and near-infrared maxima of phase ~0.05-0.13, with no lags in the minima. For three stars mid-infrared maximum appears to occur slightly before that in the near-infrared, but after optical maximum. We found three examples of secondary maxima in the rising portions of the DIRBE light curves, all of which have optical counterparts in the AAVSO data, supporting the hypothesis that they are due to shocks rather than newly formed dust layers. We found no conclusive evidence for rapid (hours to days) variations in the infrared brightnesses of these stars. Results of this work was published in Smith, et.al. (2000).

FUSE Observations of a Mira Variable Star:

This work was carried out in collaboration with Dr. Mike Castelaz. We obtained a FUSE spectrum of the long-period variable (Mira-type) star S Car. This observation gave us the opportunity to probe the temperature-density structure the outer shocked region of the atmosphere of this star using the hydrogen Lyman lines. We obtained an LWRS spectrum on 25 May 2001 when this star was at optical light-curve phase 0.35. A very weak emission feature was (possibly) seen just above the noise in this spectrum at the location of the Lyman-beta line. We made flux comparisons between Lyman lines and UV emission lines obtained at near coincident phases with the IUE. This was done to study the effect that the radiation field from the inner, hotter shocks (where Mg II and the Balmer lines form) have on the outer shocked region (where the Lyman lines form). We also made comparisons to synthetic spectra from dynamic models representative of this star. These NLTE radiative transfer calculations have shown that the radiation field of the inner shocks dominate the ionization throughout the entire atmosphere. The calculations also have shown that the Lyman emission lines form in the outer reaches of the atmosphere where the shocks are much weaker as they propagate outward. This work was presented as a poster in the 202nd AAS Meeting (see Luttermoser & Castelaz 2003a) and the "12th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun" conference proceedings article Luttermoser & Castelaz (2003b).

A High-Dispersion Spectral Atlas of Cool Red Giant Stars in the Blue and Violet:

This work was carried out during my years at ETSU, Iowa State University, and JILA. A high-dispersion spectral atlas of cool red giant stars in the blue and violet was presented in Luttermoser (2005), where the spectra were obtained over a six-year time period with the stellar spectrograph of the McMath-Pierce Telescope on Kitt Peak. Both N-type carbon stars and M-type oxygen-rich stars were presented from 3900 to 4600 Å, with the M-type stars containing both semiregular and Mira-type variables. The dominant absorption features in these stars at these wavelength result primarily from neutral metals, especially iron, and the CH and CN diatomic molecules. The Miras also showed strong emission lines during some of their pulsation cycle. Many of these emission lines result from fluorescence from the Mg II h & k lines in the UV. For these fluoresced features, comparisons are made between the Miras and the semiregular carbon-rich and oxygen-rich variables. Where the oxygen-rich semiregulars show no hint of fluorescence in these features, the carbon stars show a definite ``filling-in'' of the absorption lines.

The Biggest, Baddest, Coolest Stars Conference:

During the summer of 2007, I was the principle organizer of the conference titled The Biggest, Baddest, Coolest Stars which was published as an Astronomical Society of the Pacific Conference Series book (edited by Donald G. Luttermoser, Beverly J. Smith, and Robert E. Stencel in 2009). Details of this meeting can be found at the conference link above.

A High-Resolution UV Spectral Atlas for Mira Variable Stars (HST/STIS Spectra):

The ultraviolet (UV) spectra of Mira variable stars have been studied for nearly three decades. The International Ultraviolet Explorer (IUE) space telescope observed these stars at both low and high dispersion. Later the Hubble Space Telescope (HST) obtained high-dispersion spectra both with the High Resolution Spectrograph (HRS) and the Space Telescope Imaging Spectrograph (STIS). This paper displays a STIS spectrum of the cool Mira-type variable star R Leo taken on 31 December 1998. On this date R Leo was at phase 0.37 in its light-curve cycle. This spectrum shows a large number of emission lines and identifications are made for nearly 200 of these features. Many of these emission lines were previously unrecorded in IUE and HRS spectra of Miras, such as the Fe II (UV33, 35, 158, 160, 161, 180, 181), Mn II (UV38), V II (UV43, 73), Zr II (UV58), and the Ni II (UV36) multiplets. The electron density diagnostic multiplet of C II] (UV0.01) gives an electron density of 10⁹ cm^-3 for R Leo at this phase. This is similar to the electron density found for the Mira star R Hya at phase 0.26 obtained with a HST/HRS spectrum. Finally, the photospheric spectrum was detected from 2980 Å (the long wavelength cut-off) down to 2450 Å. Results of this work can be found at Luttermoser (2009b).

Radio Emissions from Substellar Companions of Evolved Cool Stars:

Dr. Rico Ignace, Dr. Mark Giroux, and myself carried out this study. A number of substellar companions to evolved cool stars have now been reported. Cool giants are distinct from their progenitor main-sequence low-mass stars in a number of ways. First, the mass loss rates of cool giant stars are orders of magnitude greater than for the late-type main-sequence stars. Secondly, on the cool side of the Linsky-Haisch `dividing line', K and M giant stars are not X-ray sources, although they do show evidence for chromospheres. As a result, cool star winds are largely neutral for those spectral types, suggesting that planetary or brown dwarf magnetospheres will not be effective in standing off the stellar wind. In this case, one expects the formation of a bow shock morphology at the companion, deep inside its magnetosphere. We explore radio emissions from substellar companions to giant stars using (a) the radiometric Bode's law and (b) a model for a bow shock morphology. Stars that are X-ray emitters likely have fully ionized winds, and the radio emission can be at the milli-Jansky level in favourable conditions. Non-coronal giant stars produce only micro-Jansky level emissions when adjusted for low-level ionizations. If the largely neutral flow penetrates the magnetosphere, a bow shock results that can be strong enough to ionize hydrogen. The incoherent cyclotron emission is sub-micro-Jansky. However, the long wavelength radio emission of Solar system objects is dominated by the cyclotron maser instability (CMI) mechanism. Our study leads to the following two observational prospects. First, for coronal giant stars that have ionized winds, application of the radiometic Bode's law indicates that long wavelength emission from substellar companions to giant stars may be detectable or nearly detectable with existing facilities. Secondly, for the non-coronal giant stars that have neutral winds, the resultant bow shock may act as a `feeder' of electrons that is well embedded in the companion's magnetosphere. Incoherent cyclotron emissions are far too faint to be detectable, even with next generation facilities; however, much brighter flux densities may be achievable when CMI is considered. Results of this work can be found at Ignace, Giroux, & Luttermoser (2010).

An Interferometrically Derived Sample of Miras with Phase using Spitzer:

This work was carried out by the Mira Infrared Group lead by Dr. Michelle Creech-Eakman and published in Creech-Eakman, Güth, Luttermoser, Jurgenson, and Speck (2012). We showed some preliminary 10-37 micron high-resolution spectra taken with the Spitzer Space Telescope in 2008-9 of Mira variables distributed across the M, S and C chemical subclasses. Our entire Spitzer sample of 25 galactic Miras was observed from two to several times during this observing campaign and all have simultaneously measured near-infrared interferometric diameters acquired using the Palomar Testbed Interferometer (PTI). Because our sources are very bright for Spitzer IRS (typically 5-100 Janskys), we have excellent signal to noise and for many sources see marked changes in overall flux levels as a function of phase. Further, we are able to identify many strong emission lines and emission features due to silicate and carbon dusts and molecular constituents. We introduce the sample and the design of our experiment, discuss the data reduction required for such bright sources using Spitzer, show several examples of spectra with phase and discuss some preliminary findings. Finally, we discuss future steps for Paper II, to be presented later in the year.

One can find many of my published papers by clicking this link.