Adam Jensen - Academia.edu (original) (raw)
Papers by Adam Jensen
2012 34th International Conference on Software Engineering (ICSE), 2012
... The Repository for Model Driven Development (ReMoDD) project is concerned with developing a c... more ... The Repository for Model Driven Development (ReMoDD) project is concerned with developing a community-driven repository that will contain ... that can be used as points against which MDD techniques are compared and evaluated, model and specification patterns, generic ...
We have previously presented preliminary results, based on data from the Far Ultraviolet Spectros... more We have previously presented preliminary results, based on data from the Far Ultraviolet Spectroscopic Explorer, of the column densities and velocity structure of rotationally excited (J=2 and greater) molecular hydrogen in several translucent lines of sight. Our two most interesting results were the scarcity of detections of H2 in states of J=6 and greater and little-to-no evidence of any variation in the velocity structure of H2 in different rotationally excited states, a situation which may be conceivable under certain conditions and has been previously suggested. We now present our completed analysis of a sample of 20+ lines of sight, primarily lines of sight from the FUSE Translucent Cloud Survey, and comment further on our previous results. In addition, we present our interpretation of these lines of sight, using simple but physically justified cloud models input into radiative transfer codes. While few if any of these lines of sight a dominated by a single, true "translucent cloud", understanding the physical conditions in these lines of sight is an important step toward understanding translucent clouds, which will be examined in more detail with the Cosmic Origins Spectrograph.
Despite its importance to interstellar chemistry, particularly as one of the dominant elements of... more Despite its importance to interstellar chemistry, particularly as one of the dominant elements of interstellar dust, the gas-phase abundance of silicon is somewhat poorly known. Previous surveys of interstellar silicon have been based mostly on medium-resolution IUE spectroscopy of saturated absorption lines or the weak line of Si II at 2335 angstroms. Derivation of Si II column densities is preferable through the latter method, but there have only been 7 interstellar absorption detections of this line. Therefore, previous surveys are uncertain due to either potential systematic issues or limited statistics. We explore silicon abundances through archival HST/STIS data of 46 lines of sight. Many of these lines of sight use the higher-resolution echelle gratings of STIS and the data covers several absorption lines suitable for simultaneous modeling. We use stellar models to obtain a more accurate representation of the continuum in order to properly model the Si II lines. Contrary to what is commonly assumed by some dust models, we find a nontrivial amount of the cosmic abundance of silicon to be in the gas phase ( 10% or more in many lines of sight). We also explore correlations between depletion and line of sight properties.
Astrophysical Journal, 2010
The {\it Far Ultraviolet Spectroscopic Explorer} ({\it FUSE}) has allowed precise determinations ... more The {\it Far Ultraviolet Spectroscopic Explorer} ({\it FUSE}) has allowed precise determinations of the column densities of molecular hydrogen ($\Hmol$) in Galactic lines of sight with a wide range of pathlengths and extinction properties. However, survey studies of lines of sight with greater extinction have been mostly restricted to the low-$J$ states (lower total angular momentum) in which most molecular hydrogen is observed. This paper presents a survey of column densities for the molecular hydrogen in states of greater rotational excitation ($J \geq 2$) in Galactic lines of sight with logNHmolgtrsim20\log{\NHmol} \gtrsim 20logNHmolgtrsim20. This study is comprehensive through the highest excited state detectable in each line of sight. J=5 is observed in every line of sight, and we detect J=7 in four lines of sight, J=8 in one line of sight, and vibrationally excited Hmol\HmolHmol in two lines of sight. We compared the apparent bbb-values and velocity offsets of the higher-$J$ states relative to the dominant low-$J$ states and we found no evidence of any trends that might provide insight into the formation of higher-$J$ Hmol\HmolHmol, although these results are the most affected by the limits of the {\it FUSE} resolution. We also derive excitation temperatures based on the column densities of the different states. We confirm that at least two distinct temperatures are necessary to adequately describe these lines of sight, and that more temperatures are probably necessary. Total Hmol\HmolHmol column density is known to be correlated with other molecules; we explore if correlations vary as a function of JJJ for several molecules, most importantly CH and CH$^+$. Finally, we briefly discuss interpretations of selected lines of sight by comparing them to models computed using the Meudon PDR code.
We propose to observe a sample of hot, reddened stars to measure the wavelength dependence of int... more We propose to observe a sample of hot, reddened stars to measure the wavelength dependence of interstellar extinction from 3-24 um along lines of sight probing the dense, high optical depth environments of interstellar clouds. We will use IRAC (3-8 um), IRS (low resolution, 5-21 um), IRS-PUI (15 um), and MIPS (24 um) to measure the infrared extinction curve for a sample of stars with A(V) up to ~7.5. With the installation of the Cosmic Origins Spectrograph (COS) on HST, UV observations with high S/N towards high A(V) lines of sight will possible for the first time. Spitzer provides the first opportunity to observe silicate features in the infrared along sightlines with UV extinction curves. The complementarity of the two instruments represents an unprecedented opportunity to measure extinction curves from the UV through the IR along such high optical depth lines of sight. The availability of extinction curves covering the full wavelength range from the UV through IR supplied by this program will provide a unique probe the effects of environment on grain formation, growth, and destruction. Additionally, the accurate measurement of the IR extinction curve along dense sight lines will provide insight into the nature of interstellar dust as a function of environment, both from prominent solid state features (e.g. 10/18 um silicate) and the shape of the continuum extinction.
International Conference on Software Engineering, 2012
The Repository for Model-Driven Development (ReMoDD) contains artifacts that support Model-Driven... more The Repository for Model-Driven Development (ReMoDD) contains artifacts that support Model-Driven Development (MDD) research and education. ReMoDD is collecting (1) documented MDD case studies, (2) examples of models reflecting good and bad modeling practices, (3) reference models (including metamodels) that can be used as the basis for comparing and evaluating MDD techniques, (4) generic models and transformations reflecting reusable modeling experience, (5) descriptions of modeling techniques, practices and experiences, and (6) modeling exercises and problems that can be used to develop classroom assignments and projects. ReMoDD provides a single point of access to shared artifacts reflecting high-quality MDD experience and knowledge from industry and academia. This access facilitates sharing of relevant knowledge and experience that improve MDD activities in research, education and industry.
Astrophysical Journal, 2006
We report on the abundance of interstellar neutral nitrogen (NI) for 30 sightlines, using data fr... more We report on the abundance of interstellar neutral nitrogen (NI) for 30 sightlines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Hubble Space Telescope (HST). NI column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines and subsequently fitting those to a curve of growth. We find a mean interstellar N/H of 51+/-4 ppm. This is below the mean found by Meyer et al. of 62(+4,-3) ppm (adjusted for a difference in f-values). Our mean N/H is similar, however, to the (f-value adjusted) mean of 51+/-3 ppm found by Knauth et al. for a larger sample of sightlines with larger hydrogen column densities comparable to those in this study. We discuss the question of whether or not nitrogen shows increased gas-phase depletion in lines of sight with column densities log(H_tot) >~ 21, as claimed by Knauth et al. The nitrogen abundance in the line of sight toward HD 152236 is particularly interesting. We derive very small N/H and N/O ratios for this line of sight that may support a previous suggestion that members of the Sco OB1 association formed from an N-deficient region.
Astrophysical Journal, 2004
We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from... more We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE), the International Spectroscopic Explorer (IUE), and the Hubble Space Telescope (HST). OI column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines, and subsequently fitting those to a curve of growth. We consider both our general sample of 26 sightlines and a more restrictive sample of 10 sightlines that utilize HST data for a measurement of the weak 1355 angstrom line of oxygen, and are thus better constrained due to our sampling of all three sections of the curve of growth. The column densities of our HST sample show ratios of O/H that agree with the current best solar value if dust is considered, with the possible exception of one sightline (HD 37903). We note some very limited evidence in the HST sample for trends of increasing depletion with respect to the ratio of total to selective extinction and the molecular fraction of hydrogen, but the trends are not conclusive. Unlike a recent result from Cartledge et al. (2004), we do not see evidence for increasing depletion with respect to the average volume density of hydrogen, but our HST sample contains only two points more dense than the critical density determined in that paper. The column densities of our more general sample show some scatter in O/H, but most agree with the solar value to within errors. We discuss these results in the context of establishing the best method for determining interstellar abundances, the unresolved question of the best value for O/H in the interstellar medium (ISM), the O/H ratios observed in Galactic stars, and the depletion of gas-phase oxygen onto dust grains.
Astrophysical Journal, 2007
In this paper we report on the gas-phase abundance of singly-ionized magnesium (Mg II) in 44 line... more In this paper we report on the gas-phase abundance of singly-ionized magnesium (Mg II) in 44 lines of sight, using data from the Hubble Space Telescope (HST). We measure Mg II column densities by analyzing medium- and high-resolution archival STIS spectra of the 1240 A doublet of Mg II. We find that Mg II depletion is correlated with many line of sight parameters (e.g. F(H_2), E_(B-V), E_(B-V)/r, A_V, and A_V/r) in addition to the well-known correlation with <n_H>. These parameters should be more directly related to dust content and thus have more physical significance with regard to the depletion of elements such as magnesium. We examine the significance of these additional correlations as compared to the known correlation between Mg II depletion and <n_H>. While none of the correlations are better predictors of Mg II depletion than <n_H>, some are statistically significant even assuming fixed <n_H>. We discuss the ranges over which these correlations are valid, their strength at fixed <n_H>, and physical interpretations.
Astrophysical Journal, 2007
In this paper, we report on the gas-phase abundance of singly-ionized iron (Fe II) for 51 lines o... more In this paper, we report on the gas-phase abundance of singly-ionized iron (Fe II) for 51 lines of sight, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE). Fe II column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines and subsequently fitting those to a curve of growth. Our derivation of Fe II column densities and abundances creates the largest sample of iron abundances in moderately- to highly-reddened lines of sight explored with FUSE, lines of sight that are on average more reddened than lines of sight in previous Copernicus studies. We present three major results. First, we observe the well-established correlation between iron depletion and <n_H> and also find trends between iron depletion and other line of sight parameters (e.g. f(H_2), E_(B-V), and A_V), and examine the significance of these trends. Of note, a few of our lines of sight probe larger densities than previously explored and we do not see significantly enhanced depletion effects. Second, we present two detections of an extremely weak Fe II line at 1901.773 A in the archival STIS spectra of two lines of sight (HD 24534 and HD 93222). We compare these detections to the column densities derived through FUSE spectra and comment on the line's f-value and utility for future studies of Fe II. Lastly, we present strong anecdotal evidence that the Fe II f-values derived empirically through FUSE data are more accurate than previous values that have been theoretically calculated, with the probable exception of f_1112.
Astrophysical Journal, 2003
We investigate the relationship between the dark matter and baryons in the linear regime. This re... more We investigate the relationship between the dark matter and baryons in the linear regime. This relation is quantified by the so-called ``filtering scale.'' We show that a simple Gaussian Ansatz that uses the filtering scale provides a good approximation to the exact solution.
We investigate the relationship between the dark matter and baryons in the linear regime. This re... more We investigate the relationship between the dark matter and baryons in the linear regime. This relation is quantified by the so-called '' filtering scale.'' We show that a simple Gaussian Ansatz that uses the filtering scale provides a good approximation to the exact solution. Subject headings: cosmic microwave background -cosmology: theory -galaxies: formationintergalactic medium -large-scale structure of universe
Astrophysical Journal, 2008
We have used archival FUSE data to complete a survey of interstellar HD in 41 lines of sight with... more We have used archival FUSE data to complete a survey of interstellar HD in 41 lines of sight with a wide range of extinctions. This follow up to an earlier survey was made to further assess the utility of HD as a cosmological probe; to analyze the HD formation process; and to see what trends with other interstellar properties were present in the data. We employed the curve-of-growth method, supported by line profile fitting, to derive accurate column densities of HD. We find that the N(HD)/2N(H2) ratio is substantially lower than the atomic D/H ratio and conclude that the molecular ratio has no bearing on cosmology, because local processes are responsible for the formation of HD. Based on correlations with E(B-V), H2, CO, and iron depletion, we find that HD is formed in the densest portion of the clouds; the slope of the logN(HD)/log(H2) correlation is greater than 1.0, caused by the destruction rate of HD declining more slowly than that of H2; and, as a sidelight, that the depletions are density dependent.
The number of exoplanets with detected atmospheres is rapidly increasing. Particularly intriguing... more The number of exoplanets with detected atmospheres is rapidly increasing. Particularly intriguing are detections of hydrogen that are attributed to the upper, unbound portion of their atmospheres (i.e. the "exospheres") and indicate that some gas giants may be evaporating. Exospheric hydrogen has only been detected in Lyman-alpha, which, as with all single line detections, only provides limited information about physical conditions such as density and temperature. A much better understanding of exospheres and their evolution would be gained through a constraint on H-alpha. We have obtained more than 100 total hours of spectroscopic observations with the Hobby-Eberly Telescope of five different exoplanetary targets, with the goal of deriving transmission spectra of exoplanetary atmospheres; two of these targets have had their exospheres detected in Lyman-alpha. Here we report on our search for H-alpha absorption in these exospheres, and the implications for their physical conditions and evolution. This work is supported by the National Science Foundation through an Astronomy and Astrophysics Research Grant (AST-0903573). The Hobby-Eberly Telescope is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen and is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.
We present the first results of W[HE]2ATS2 (The Wesleyan Hobby-Eberly High-resolution Exoplanetar... more We present the first results of W[HE]2ATS2 (The Wesleyan Hobby-Eberly High-resolution Exoplanetary Atmospheric Transmission Spectroscopy Survey). To date, this survey has collected approximately 90 hours worth of high-resolution (R 60k) ground-based optical spectra with the 9.2m Hobby-Eberly Telescope, with additional observations in progress. The survey includes five different solar-type stellar systems with transiting hot Jupiters or Neptunes. Spectra are taken both in and out of transit; the two categories of observations are each coadded with the resulting coadded spectra differenced to search for absorption from resonance lines of alkali metals that are expected in these atmospheres. We will present our confirmation of previous detections of Na I absorption in HD 189733 and HD 209458 and present upper limits on and possible new detections of Na I and K I in these and other targets. In addition, we will describe the details and challenges of our data reduction and analysis. Finally, we will discuss our prospects for future work in searching for additional alkali metal lines and exospheric absorption. This work is supported by the National Science Foundation through an Astronomy and Astrophysics Research Grant (AST-0903573). The Hobby-Eberly Telescope is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen and is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.
The Astrophysical Journal, 2012
The Astrophysical Journal, 2007
We report results from a survey of neutral fluorine (F I) in the interstellar medium. Data from t... more We report results from a survey of neutral fluorine (F I) in the interstellar medium. Data from the Far Ultraviolet Spectroscopic Explorer (FUSE) were used to analyze 26 lines of sight lying both in the galactic disk and halo, including lines to Wolf-Rayet stars and through known supernova remnants. The equivalent widths of fluorine resonance lines at 951.871Å and 954.827Å were measured or assigned upper limits and combined with a nitrogen curve of growth to obtain F I column densities. These column densities were then used to calculate fluorine depletions. Comparisons are made to the previous study of F I by and implications for F I formation and depletion are discussed.
The Astrophysical Journal, 2005
We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from... more We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE), the International Spectroscopic Explorer (IUE), and the Hubble Space Telescope (HST). OI column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines, and subsequently fitting those to a curve of growth. We consider both our general sample of 26 sightlines and a more restrictive sample of 10 sightlines that utilize HST data for a measurement of the weak 1355Å line of oxygen, and are thus better constrained due to our sampling of all three sections of the curve of growth. The column densities of our HST sample show ratios of O/H that agree with the current best solar value if dust is considered, with the possible exception of one sightline (HD 37903). We note some very limited evidence in the HST sample for trends of increasing depletion with respect to R V and f (H 2 ), but the trends are not conclusive. Unlike a recent result from Cartledge et al. , we do not see evidence for increasing depletion with respect to n H , but our HST sample contains only two points more dense than the critical density determined in that paper. The column densities of our more general sample show some scatter in O/H, but most agree with the solar value to within errors. We discuss these results in the context of establishing the best method for determining interstellar abundances, the unresolved question of the best value for O/H in the interstellar medium (ISM), the O/H ratios observed in Galactic stars, and the depletion of gas-phase oxygen onto dust grains. Subject headings: ISM: abundances -ISM: depletions -ultraviolet: ISM Keenan et al. (1985) explored 26 sightlines-including one sightline from York et al. Cartledge et al. (2001) examined 11 sightlines using the Space Telescope Imaging Spectrograph (STIS) onboard HST to observe the 1355Å line. This study used two methods: profile fitting, where velocity information from other atomic species is incorporated into the fit of the oxygen line; and the apparent optical depth (AOD) method, where it is as-
The Astrophysical Journal, 2010
The Far Ultraviolet Spectroscopic Explorer (FUSE) has allowed precise determinations of the colum... more The Far Ultraviolet Spectroscopic Explorer (FUSE) has allowed precise determinations of the column densities of molecular hydrogen (H 2 ) in Galactic lines of sight with a wide range of pathlengths and extinction properties. However, survey studies of lines of sight with greater extinction have been mostly restricted to the low-J states (lower total angular momentum) in which most molecular hydrogen is observed. This paper presents a survey of column densities for the molecular hydrogen in states of greater rotational excitation (J ≥ 2) in Galactic lines of sight with log N(H 2 ) 20. This study is comprehensive through the highest excited state detectable in each line of sight. J = 5 is observed in every line of sight, and we detect J = 7 in four lines of sight, J = 8 in one line of sight, and vibrationally excited H 2 in two lines of sight. We compared the apparent b-values and velocity offsets of the higher-J states relative to the dominant low-J states and we found no evidence of any trends that might provide insight into the formation of higher-J H 2 , although these results are the most affected by the limits of the FUSE resolution. We also derive excitation temperatures based on the column densities of the different states. We confirm that at least two distinct temperatures are necessary to adequately describe these lines of sight, and that more temperatures are probably necessary. Total H 2 column density is known to be correlated with other molecules; we explore if correlations vary as a function of J for several molecules, most importantly CH and CH + . Finally, we briefly discuss interpretations of selected lines of sight by comparing them to models computed using the Meudon PDR code.
2012 34th International Conference on Software Engineering (ICSE), 2012
... The Repository for Model Driven Development (ReMoDD) project is concerned with developing a c... more ... The Repository for Model Driven Development (ReMoDD) project is concerned with developing a community-driven repository that will contain ... that can be used as points against which MDD techniques are compared and evaluated, model and specification patterns, generic ...
We have previously presented preliminary results, based on data from the Far Ultraviolet Spectros... more We have previously presented preliminary results, based on data from the Far Ultraviolet Spectroscopic Explorer, of the column densities and velocity structure of rotationally excited (J=2 and greater) molecular hydrogen in several translucent lines of sight. Our two most interesting results were the scarcity of detections of H2 in states of J=6 and greater and little-to-no evidence of any variation in the velocity structure of H2 in different rotationally excited states, a situation which may be conceivable under certain conditions and has been previously suggested. We now present our completed analysis of a sample of 20+ lines of sight, primarily lines of sight from the FUSE Translucent Cloud Survey, and comment further on our previous results. In addition, we present our interpretation of these lines of sight, using simple but physically justified cloud models input into radiative transfer codes. While few if any of these lines of sight a dominated by a single, true "translucent cloud", understanding the physical conditions in these lines of sight is an important step toward understanding translucent clouds, which will be examined in more detail with the Cosmic Origins Spectrograph.
Despite its importance to interstellar chemistry, particularly as one of the dominant elements of... more Despite its importance to interstellar chemistry, particularly as one of the dominant elements of interstellar dust, the gas-phase abundance of silicon is somewhat poorly known. Previous surveys of interstellar silicon have been based mostly on medium-resolution IUE spectroscopy of saturated absorption lines or the weak line of Si II at 2335 angstroms. Derivation of Si II column densities is preferable through the latter method, but there have only been 7 interstellar absorption detections of this line. Therefore, previous surveys are uncertain due to either potential systematic issues or limited statistics. We explore silicon abundances through archival HST/STIS data of 46 lines of sight. Many of these lines of sight use the higher-resolution echelle gratings of STIS and the data covers several absorption lines suitable for simultaneous modeling. We use stellar models to obtain a more accurate representation of the continuum in order to properly model the Si II lines. Contrary to what is commonly assumed by some dust models, we find a nontrivial amount of the cosmic abundance of silicon to be in the gas phase ( 10% or more in many lines of sight). We also explore correlations between depletion and line of sight properties.
Astrophysical Journal, 2010
The {\it Far Ultraviolet Spectroscopic Explorer} ({\it FUSE}) has allowed precise determinations ... more The {\it Far Ultraviolet Spectroscopic Explorer} ({\it FUSE}) has allowed precise determinations of the column densities of molecular hydrogen ($\Hmol$) in Galactic lines of sight with a wide range of pathlengths and extinction properties. However, survey studies of lines of sight with greater extinction have been mostly restricted to the low-$J$ states (lower total angular momentum) in which most molecular hydrogen is observed. This paper presents a survey of column densities for the molecular hydrogen in states of greater rotational excitation ($J \geq 2$) in Galactic lines of sight with logNHmolgtrsim20\log{\NHmol} \gtrsim 20logNHmolgtrsim20. This study is comprehensive through the highest excited state detectable in each line of sight. J=5 is observed in every line of sight, and we detect J=7 in four lines of sight, J=8 in one line of sight, and vibrationally excited Hmol\HmolHmol in two lines of sight. We compared the apparent bbb-values and velocity offsets of the higher-$J$ states relative to the dominant low-$J$ states and we found no evidence of any trends that might provide insight into the formation of higher-$J$ Hmol\HmolHmol, although these results are the most affected by the limits of the {\it FUSE} resolution. We also derive excitation temperatures based on the column densities of the different states. We confirm that at least two distinct temperatures are necessary to adequately describe these lines of sight, and that more temperatures are probably necessary. Total Hmol\HmolHmol column density is known to be correlated with other molecules; we explore if correlations vary as a function of JJJ for several molecules, most importantly CH and CH$^+$. Finally, we briefly discuss interpretations of selected lines of sight by comparing them to models computed using the Meudon PDR code.
We propose to observe a sample of hot, reddened stars to measure the wavelength dependence of int... more We propose to observe a sample of hot, reddened stars to measure the wavelength dependence of interstellar extinction from 3-24 um along lines of sight probing the dense, high optical depth environments of interstellar clouds. We will use IRAC (3-8 um), IRS (low resolution, 5-21 um), IRS-PUI (15 um), and MIPS (24 um) to measure the infrared extinction curve for a sample of stars with A(V) up to ~7.5. With the installation of the Cosmic Origins Spectrograph (COS) on HST, UV observations with high S/N towards high A(V) lines of sight will possible for the first time. Spitzer provides the first opportunity to observe silicate features in the infrared along sightlines with UV extinction curves. The complementarity of the two instruments represents an unprecedented opportunity to measure extinction curves from the UV through the IR along such high optical depth lines of sight. The availability of extinction curves covering the full wavelength range from the UV through IR supplied by this program will provide a unique probe the effects of environment on grain formation, growth, and destruction. Additionally, the accurate measurement of the IR extinction curve along dense sight lines will provide insight into the nature of interstellar dust as a function of environment, both from prominent solid state features (e.g. 10/18 um silicate) and the shape of the continuum extinction.
International Conference on Software Engineering, 2012
The Repository for Model-Driven Development (ReMoDD) contains artifacts that support Model-Driven... more The Repository for Model-Driven Development (ReMoDD) contains artifacts that support Model-Driven Development (MDD) research and education. ReMoDD is collecting (1) documented MDD case studies, (2) examples of models reflecting good and bad modeling practices, (3) reference models (including metamodels) that can be used as the basis for comparing and evaluating MDD techniques, (4) generic models and transformations reflecting reusable modeling experience, (5) descriptions of modeling techniques, practices and experiences, and (6) modeling exercises and problems that can be used to develop classroom assignments and projects. ReMoDD provides a single point of access to shared artifacts reflecting high-quality MDD experience and knowledge from industry and academia. This access facilitates sharing of relevant knowledge and experience that improve MDD activities in research, education and industry.
Astrophysical Journal, 2006
We report on the abundance of interstellar neutral nitrogen (NI) for 30 sightlines, using data fr... more We report on the abundance of interstellar neutral nitrogen (NI) for 30 sightlines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Hubble Space Telescope (HST). NI column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines and subsequently fitting those to a curve of growth. We find a mean interstellar N/H of 51+/-4 ppm. This is below the mean found by Meyer et al. of 62(+4,-3) ppm (adjusted for a difference in f-values). Our mean N/H is similar, however, to the (f-value adjusted) mean of 51+/-3 ppm found by Knauth et al. for a larger sample of sightlines with larger hydrogen column densities comparable to those in this study. We discuss the question of whether or not nitrogen shows increased gas-phase depletion in lines of sight with column densities log(H_tot) >~ 21, as claimed by Knauth et al. The nitrogen abundance in the line of sight toward HD 152236 is particularly interesting. We derive very small N/H and N/O ratios for this line of sight that may support a previous suggestion that members of the Sco OB1 association formed from an N-deficient region.
Astrophysical Journal, 2004
We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from... more We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE), the International Spectroscopic Explorer (IUE), and the Hubble Space Telescope (HST). OI column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines, and subsequently fitting those to a curve of growth. We consider both our general sample of 26 sightlines and a more restrictive sample of 10 sightlines that utilize HST data for a measurement of the weak 1355 angstrom line of oxygen, and are thus better constrained due to our sampling of all three sections of the curve of growth. The column densities of our HST sample show ratios of O/H that agree with the current best solar value if dust is considered, with the possible exception of one sightline (HD 37903). We note some very limited evidence in the HST sample for trends of increasing depletion with respect to the ratio of total to selective extinction and the molecular fraction of hydrogen, but the trends are not conclusive. Unlike a recent result from Cartledge et al. (2004), we do not see evidence for increasing depletion with respect to the average volume density of hydrogen, but our HST sample contains only two points more dense than the critical density determined in that paper. The column densities of our more general sample show some scatter in O/H, but most agree with the solar value to within errors. We discuss these results in the context of establishing the best method for determining interstellar abundances, the unresolved question of the best value for O/H in the interstellar medium (ISM), the O/H ratios observed in Galactic stars, and the depletion of gas-phase oxygen onto dust grains.
Astrophysical Journal, 2007
In this paper we report on the gas-phase abundance of singly-ionized magnesium (Mg II) in 44 line... more In this paper we report on the gas-phase abundance of singly-ionized magnesium (Mg II) in 44 lines of sight, using data from the Hubble Space Telescope (HST). We measure Mg II column densities by analyzing medium- and high-resolution archival STIS spectra of the 1240 A doublet of Mg II. We find that Mg II depletion is correlated with many line of sight parameters (e.g. F(H_2), E_(B-V), E_(B-V)/r, A_V, and A_V/r) in addition to the well-known correlation with <n_H>. These parameters should be more directly related to dust content and thus have more physical significance with regard to the depletion of elements such as magnesium. We examine the significance of these additional correlations as compared to the known correlation between Mg II depletion and <n_H>. While none of the correlations are better predictors of Mg II depletion than <n_H>, some are statistically significant even assuming fixed <n_H>. We discuss the ranges over which these correlations are valid, their strength at fixed <n_H>, and physical interpretations.
Astrophysical Journal, 2007
In this paper, we report on the gas-phase abundance of singly-ionized iron (Fe II) for 51 lines o... more In this paper, we report on the gas-phase abundance of singly-ionized iron (Fe II) for 51 lines of sight, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE). Fe II column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines and subsequently fitting those to a curve of growth. Our derivation of Fe II column densities and abundances creates the largest sample of iron abundances in moderately- to highly-reddened lines of sight explored with FUSE, lines of sight that are on average more reddened than lines of sight in previous Copernicus studies. We present three major results. First, we observe the well-established correlation between iron depletion and <n_H> and also find trends between iron depletion and other line of sight parameters (e.g. f(H_2), E_(B-V), and A_V), and examine the significance of these trends. Of note, a few of our lines of sight probe larger densities than previously explored and we do not see significantly enhanced depletion effects. Second, we present two detections of an extremely weak Fe II line at 1901.773 A in the archival STIS spectra of two lines of sight (HD 24534 and HD 93222). We compare these detections to the column densities derived through FUSE spectra and comment on the line's f-value and utility for future studies of Fe II. Lastly, we present strong anecdotal evidence that the Fe II f-values derived empirically through FUSE data are more accurate than previous values that have been theoretically calculated, with the probable exception of f_1112.
Astrophysical Journal, 2003
We investigate the relationship between the dark matter and baryons in the linear regime. This re... more We investigate the relationship between the dark matter and baryons in the linear regime. This relation is quantified by the so-called ``filtering scale.'' We show that a simple Gaussian Ansatz that uses the filtering scale provides a good approximation to the exact solution.
We investigate the relationship between the dark matter and baryons in the linear regime. This re... more We investigate the relationship between the dark matter and baryons in the linear regime. This relation is quantified by the so-called '' filtering scale.'' We show that a simple Gaussian Ansatz that uses the filtering scale provides a good approximation to the exact solution. Subject headings: cosmic microwave background -cosmology: theory -galaxies: formationintergalactic medium -large-scale structure of universe
Astrophysical Journal, 2008
We have used archival FUSE data to complete a survey of interstellar HD in 41 lines of sight with... more We have used archival FUSE data to complete a survey of interstellar HD in 41 lines of sight with a wide range of extinctions. This follow up to an earlier survey was made to further assess the utility of HD as a cosmological probe; to analyze the HD formation process; and to see what trends with other interstellar properties were present in the data. We employed the curve-of-growth method, supported by line profile fitting, to derive accurate column densities of HD. We find that the N(HD)/2N(H2) ratio is substantially lower than the atomic D/H ratio and conclude that the molecular ratio has no bearing on cosmology, because local processes are responsible for the formation of HD. Based on correlations with E(B-V), H2, CO, and iron depletion, we find that HD is formed in the densest portion of the clouds; the slope of the logN(HD)/log(H2) correlation is greater than 1.0, caused by the destruction rate of HD declining more slowly than that of H2; and, as a sidelight, that the depletions are density dependent.
The number of exoplanets with detected atmospheres is rapidly increasing. Particularly intriguing... more The number of exoplanets with detected atmospheres is rapidly increasing. Particularly intriguing are detections of hydrogen that are attributed to the upper, unbound portion of their atmospheres (i.e. the "exospheres") and indicate that some gas giants may be evaporating. Exospheric hydrogen has only been detected in Lyman-alpha, which, as with all single line detections, only provides limited information about physical conditions such as density and temperature. A much better understanding of exospheres and their evolution would be gained through a constraint on H-alpha. We have obtained more than 100 total hours of spectroscopic observations with the Hobby-Eberly Telescope of five different exoplanetary targets, with the goal of deriving transmission spectra of exoplanetary atmospheres; two of these targets have had their exospheres detected in Lyman-alpha. Here we report on our search for H-alpha absorption in these exospheres, and the implications for their physical conditions and evolution. This work is supported by the National Science Foundation through an Astronomy and Astrophysics Research Grant (AST-0903573). The Hobby-Eberly Telescope is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen and is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.
We present the first results of W[HE]2ATS2 (The Wesleyan Hobby-Eberly High-resolution Exoplanetar... more We present the first results of W[HE]2ATS2 (The Wesleyan Hobby-Eberly High-resolution Exoplanetary Atmospheric Transmission Spectroscopy Survey). To date, this survey has collected approximately 90 hours worth of high-resolution (R 60k) ground-based optical spectra with the 9.2m Hobby-Eberly Telescope, with additional observations in progress. The survey includes five different solar-type stellar systems with transiting hot Jupiters or Neptunes. Spectra are taken both in and out of transit; the two categories of observations are each coadded with the resulting coadded spectra differenced to search for absorption from resonance lines of alkali metals that are expected in these atmospheres. We will present our confirmation of previous detections of Na I absorption in HD 189733 and HD 209458 and present upper limits on and possible new detections of Na I and K I in these and other targets. In addition, we will describe the details and challenges of our data reduction and analysis. Finally, we will discuss our prospects for future work in searching for additional alkali metal lines and exospheric absorption. This work is supported by the National Science Foundation through an Astronomy and Astrophysics Research Grant (AST-0903573). The Hobby-Eberly Telescope is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen and is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.
The Astrophysical Journal, 2012
The Astrophysical Journal, 2007
We report results from a survey of neutral fluorine (F I) in the interstellar medium. Data from t... more We report results from a survey of neutral fluorine (F I) in the interstellar medium. Data from the Far Ultraviolet Spectroscopic Explorer (FUSE) were used to analyze 26 lines of sight lying both in the galactic disk and halo, including lines to Wolf-Rayet stars and through known supernova remnants. The equivalent widths of fluorine resonance lines at 951.871Å and 954.827Å were measured or assigned upper limits and combined with a nitrogen curve of growth to obtain F I column densities. These column densities were then used to calculate fluorine depletions. Comparisons are made to the previous study of F I by and implications for F I formation and depletion are discussed.
The Astrophysical Journal, 2005
We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from... more We report on the abundance of interstellar neutral oxygen (OI) for 26 sightlines, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE), the International Spectroscopic Explorer (IUE), and the Hubble Space Telescope (HST). OI column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines, and subsequently fitting those to a curve of growth. We consider both our general sample of 26 sightlines and a more restrictive sample of 10 sightlines that utilize HST data for a measurement of the weak 1355Å line of oxygen, and are thus better constrained due to our sampling of all three sections of the curve of growth. The column densities of our HST sample show ratios of O/H that agree with the current best solar value if dust is considered, with the possible exception of one sightline (HD 37903). We note some very limited evidence in the HST sample for trends of increasing depletion with respect to R V and f (H 2 ), but the trends are not conclusive. Unlike a recent result from Cartledge et al. , we do not see evidence for increasing depletion with respect to n H , but our HST sample contains only two points more dense than the critical density determined in that paper. The column densities of our more general sample show some scatter in O/H, but most agree with the solar value to within errors. We discuss these results in the context of establishing the best method for determining interstellar abundances, the unresolved question of the best value for O/H in the interstellar medium (ISM), the O/H ratios observed in Galactic stars, and the depletion of gas-phase oxygen onto dust grains. Subject headings: ISM: abundances -ISM: depletions -ultraviolet: ISM Keenan et al. (1985) explored 26 sightlines-including one sightline from York et al. Cartledge et al. (2001) examined 11 sightlines using the Space Telescope Imaging Spectrograph (STIS) onboard HST to observe the 1355Å line. This study used two methods: profile fitting, where velocity information from other atomic species is incorporated into the fit of the oxygen line; and the apparent optical depth (AOD) method, where it is as-
The Astrophysical Journal, 2010
The Far Ultraviolet Spectroscopic Explorer (FUSE) has allowed precise determinations of the colum... more The Far Ultraviolet Spectroscopic Explorer (FUSE) has allowed precise determinations of the column densities of molecular hydrogen (H 2 ) in Galactic lines of sight with a wide range of pathlengths and extinction properties. However, survey studies of lines of sight with greater extinction have been mostly restricted to the low-J states (lower total angular momentum) in which most molecular hydrogen is observed. This paper presents a survey of column densities for the molecular hydrogen in states of greater rotational excitation (J ≥ 2) in Galactic lines of sight with log N(H 2 ) 20. This study is comprehensive through the highest excited state detectable in each line of sight. J = 5 is observed in every line of sight, and we detect J = 7 in four lines of sight, J = 8 in one line of sight, and vibrationally excited H 2 in two lines of sight. We compared the apparent b-values and velocity offsets of the higher-J states relative to the dominant low-J states and we found no evidence of any trends that might provide insight into the formation of higher-J H 2 , although these results are the most affected by the limits of the FUSE resolution. We also derive excitation temperatures based on the column densities of the different states. We confirm that at least two distinct temperatures are necessary to adequately describe these lines of sight, and that more temperatures are probably necessary. Total H 2 column density is known to be correlated with other molecules; we explore if correlations vary as a function of J for several molecules, most importantly CH and CH + . Finally, we briefly discuss interpretations of selected lines of sight by comparing them to models computed using the Meudon PDR code.