14 research outputs found
Revisiting the Temperature of the Diffuse ISM with CHESS Sounding Rocket Observations
Measuring the temperature and abundance patterns of clouds in the
interstellar medium (ISM) provides an observational basis for models of the
physical conditions within the clouds, which play an important role in studies
of star and planet formation. The Colorado High-resolution Echelle Stellar
Spectrograph (CHESS) is a far ultraviolet rocket-borne instrument designed to
study the atomic-to-molecular transitions within diffuse molecular and
translucent cloud regions. The final two flights of the instrument observed
Scorpii ( Sco) and Arae. We present flight results
of interstellar molecular hydrogen (H) excitation on the sightlines,
including measurements of the column densities and temperatures. These results
are compared to previous values that were measured using the damping wings of
low J H absorption features (Savage et al. 1977).
For Sco, we find that the derived column density of the J = 1 rotational level differs by a factor of 2-3 when compared to the
previous observations. We discuss the discrepancies between the two
measurements and show that the source of the difference is due to the opacity
of higher rotational levels contributing to the J = 1
absorption wing, increasing the inferred column density in the previous work.
We extend this analysis to 9 and 13 spectra to explore the
interdependence of the column densities of different rotational levels and how
the H kinetic temperature is influenced by these relationships. We
find a revised average gas kinetic temperature of the diffuse molecular ISM of
T = 68 13 K, 12% lower than the value found previously.Comment: 20 pages, 10 Figures, Accepted in Ap
Recommended from our members
The Chess Sounding Rocket: Interstellar H2 Towards Beta Scorpii and Gamma Arae
We describe the scientific motivation, technical development, and flight performance of the Colorado High-resolution Echelle Stellar Spectrograph (CHESS). CHESS is a far ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium. CHESS is an objective echelle spectrograph, which uses a mechanically-ruled echelle, a powered (f/12.4) cross-dispersing grating, and a cross-strip anode microchannel plate detector, and is designed to achieve a resolving power R > 100,000 over the bandpass λ λ 1000--1600 Å. The final two flights of the instrument (CHESS-3 and CHESS-4) observed β1; Scorpii β Sco and γ Arae (γ Ara). For CHESS-4, we describe our novel method for increasing the resolution of the instrument by physically stressing the echelle grating, introducing a curvature to the surface of the optic. We present flight results of interstellar molecular hydrogen absorption, including measurements of the column densities and temperatures, on the sightlines. For β Sco, we find that the derived column density of the J'' = 1 rotational level differs by a factor of 2--3 when compared to the previous observations of Savage et al. (1977). We discuss the discrepancies between the two measurements and show that the source of the difference is likely due to the opacity of higher rotational levels contributing to the J'' = 1 absorption wing, increasing the inferred column density in the previous work. We extend this analysis to 9 Copernicus and 13 FUSE spectra to explore the interdependence of the column densities of different J'' levels and how the H2 kinetic temperature is influenced by these relationships. Based off of our results, we find a revised average gas kinetic temperature of the diffuse ISM of T01 = 68 ± 13 K, 12% lower than the value found in the previous work.</p
Revisiting the Temperature of the Diffuse ISM with CHESS Sounding Rocket Observations
Measuring the temperature and abundance patterns of clouds in the interstellar medium (ISM) provides an observational basis for models of the physical conditions within the clouds, which play an important role in studies of star and planet formation. The Colorado High-resolution Echelle Stellar Spectrograph is a far-ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within diffuse molecular and translucent cloud regions. The final two flights of the instrument observed β^1 Scorpii (β Sco) and γ Arae. We present flight results of interstellar molecular hydrogen excitation on the sightlines, including measurements of the column densities and temperatures. These results are compared to previous values that were measured using the damping wings of low J'' H_2 absorption features. For β Sco, we find that the derived column density of the J'' = 1 rotational level differs by a factor of 2–3 when compared to the previous observations. We discuss the discrepancies between the two measurements and show that the source of the difference is due to the opacity of higher rotational levels contributing to the J'' = 1 absorption wing, increasing the inferred column density in the previous work. We extend this analysis to 9 Copernicus and 13 Far-Ultraviolet Spectroscopic Explorer spectra to explore the interdependence of the column densities of different rotational levels and how the H_2 kinetic temperature is influenced by these relationships. We find a revised average gas kinetic temperature of the diffuse molecular ISM of T_(01) = 68 ± 13 K, 12% lower than the value found previously
The fourth flight of CHESS: spectral resolution enhancements for high-resolution FUV spectroscopy
In this proceeding, we describe the scientific motivation and technical development of the Colorado Highresolution Echelle Stellar Spectrograph (CHESS), focusing on the hardware advancements and testing of components for the fourth and final launch of the payload (CHESS-4). CHESS is a far ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium. CHESS is an objective echelle spectrograph, which uses a mechanically-ruled echelle and a powered (f/12.4) cross-dispersing grating; it is designed to achieve a resolving power R > 100,000 over the band pass λλ 1000–1600 Å. CHESS-4 utilizes a 40 mm-diameter cross-strip anode readout microchannel plate detector, fabricated by Sensor Sciences LLC, to achieve high spatial resolution with high global count rate capabilities (∼ MHz). An error in the fabrication of the cross disperser limited the achievable resolution on previous launches of the payload to R ∼ 4000. To remedy this for CHESS-4, we physically stress the echelle grating, introducing a shallow toroidal curvature to the surface of the optic. Preliminary laboratory measurements of the resulting spectrum show a factor of 4–5 improvement to the resolving power. Results from final efficiency and reflectivity measurements for the optical components of CHESS-4 are presented, along with the pre-flight laboratory spectra and calibration results. CHESS-4 launched on 17 April 2018 aboard NASA/University of Colorado Boulder sounding rocket mission 36.333 UG. We present flight results for the observation of the γ Ara sightline
CIV Emission and the Ultraviolet through X-ray Spectral Energy Distribution of Radio-Quiet Quasars
In the restframe UV, two of the parameters that best characterize the range
of emission-line properties in quasar broad emission-line regions are the
equivalent width and the blueshift of the CIV line relative to the quasar rest
frame. We explore the connection between these emission-line properties and the
UV through X-ray spectral energy distribution (SED) for radio-quiet (RQ)
quasars. Our sample consists of a heterogeneous compilation of 406 quasars from
the Sloan Digital Sky Survey and Palomar-Green survey that have well-measured
CIV emission-line and X-ray properties (including 164 objects with measured
Gamma). We find that RQ quasars with both strong CIV emission and small CIV
blueshifts can be classified as "hard-spectrum" sources that are (relatively)
strong in the X-ray as compared to the UV. On the other hand, RQ quasars with
both weak CIV emission and large CIV blueshifts are instead "soft-spectrum"
sources that are (relatively) weak in the X-ray as compared to the UV. This
work helps to further bridge optical/soft X-ray "Eigenvector 1" relationships
to the UV and hard X-ray. Based on these findings, we argue that future work
should consider systematic errors in bolometric corrections (and thus accretion
rates) that are derived from a single mean SED. Detailed analysis of the CIV
emission line may allow for SED-dependent corrections to these quantities.Comment: AJ, in press; 39 pages, 11 figures, 3 table
Unification of Luminous Type 1 Quasars through CIV Emission
Using a sample of 30,000 quasars from SDSS-DR7, we explore the range of
properties exhibited by high-ionization, broad emission lines, such as CIV
1549. Specifically we investigate the anti-correlation between L_UV and
emission line EQW (the Baldwin Effect) and the "blueshifting" of
high-ionization emission lines. The blueshift of the CIV emission line is
nearly ubiquitous, with a mean shift of 810 km/s for radio-quiet (RQ) quasars
and 360 km/s for radio-loud (RL) quasars, and the Baldwin Effect is present in
both RQ and RL samples. Composite spectra are constructed as a function of CIV
emission line properties in attempt to reveal empirical relationships between
different line species and the SED. Within a two-component disk+wind model of
the broad emission line region (BELR), where the wind filters the continuum
seen by the disk component, we find that RL quasars are consistent with being
dominated by the disk component, while BALQSOs are consistent with being
dominated by the wind component. Some RQ objects have emission line features
similar to RL quasars; they may simply have insufficient black hole (BH) spin
to form radio jets. Our results suggest that there could be significant
systematic errors in the determination of L_bol and BH mass that make it
difficult to place these findings in a more physical context. However, it is
possible to classify quasars in a paradigm where the diversity of BELR
parameters are due to differences in an accretion disk wind between quasars
(and over time); these differences are underlain primarily by the SED, which
ultimately must be tied to BH mass and accretion rate.Comment: 51 pages, 18 figures, accepted by AJ, revised version includes
various modifications based on the referee's comment