scholarly journals 12C/13C Ratios and Li Abundances in Low-Mass C Stars

2000 ◽  
Vol 177 ◽  
pp. 89-95
Author(s):  
Carlos Abia ◽  
Jordi Isern
Keyword(s):  
High Resolution ◽  
Carbon Isotope ◽  
Signal To Noise Ratio ◽  
Isotope Ratios ◽  
High Signal ◽  
Isotopic Ratios ◽  
Signal To Noise ◽  
Carbon Isotope Ratios ◽  
Low Mass ◽  
Noise Ratio

High-resolution and high signal-to-noise-ratio spectroscopy is used to derive 12C/13C ratios from the Red System of the CN molecule at 8000 Å in several galactic low-mass C stars previously analyzed for lithium. It is found that Li-rich C stars usually have low isotopic ratios (< 15). This suggests that the Li and 13C enrichments in C stars might be produced by a similar mechanism. However, due to the large uncertainties in the abundance derivations for both Li and carbon isotope ratios, this result must be confirmed with further studies.

scholarly journals High Signal-To-Noise Ratio - the Spectroscopic Key to Algol Systems

1989 ◽  
Vol 107 ◽  
pp. 245-255
Author(s):  
Jocelyn Tomkin
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Signal To Noise Ratio ◽  
Large Fraction ◽  
High Signal ◽  
Signal To Noise ◽  
Algol System ◽  
Low Mass ◽  
Noise Ratio ◽  
Cno Abundances

AbstractThe usefulness of high signal-to-noise-ratio spectra for both radial-velocity and abundance studies of Algol systems is emphasised. It is shown that division by a hot star is a worthwhile step in pursuit of this objective. A preliminary analysis of high signal-to-noise-ratio, red and near-infrared, Reticon observations of R CMa shows that its primary has solar CNO abundances within the 0.3 dex observational error. The low-mass (0.17 m⊙) secondary of this Algol system must have lost a large fraction of its original mass. Some of this material would have been extensively processed during the secondary’s main-sequence lifetime and would therefore have had a highly non-solar CNO-abundance distribution. The lack of serious contamination of the primary’s abundances is consistent with most, but not all, plausible mass-transfer scenarios.

scholarly journals Seismology of southern Be stars

1994 ◽  
Vol 162 ◽  
pp. 104-105
Author(s):  
Eduardo Janot-Pacheco ◽  
Nelson Vani Leister
Keyword(s):  
High Resolution ◽  
Signal To Noise Ratio ◽  
Ccd Camera ◽  
High Signal ◽  
Be Stars ◽  
Signal To Noise ◽  
Photometric Variability ◽  
Spectroscopic Observations ◽  
Photometric Observations ◽  
Noise Ratio

We have started in 1990 a search for moving bumps in the HeI λ 667.8 nm of mainly southern, bright Be stars. The objects of our sample have been selected on the basis of photometric variability (Cuypers et al., 1989). High resolution (R≥ 30,000), high signal-to-noise ratio (S/R≥ 300) spectroscopic observations have been performed at the brazilian Laboratório Nacional de Astrofísica with a CCD camera attached to the coudé spectrograph of the 1.60 m telescope (e.g. Table I). Several hundred spectra have been taken during the last three years. Photometric observations simultaneous with spectroscopy were made on the same site in July 1992 with a two-channel photometer (Stromgren b filter) and a CCD camera (Johnson B filter) installed at two 0.60 m telescopes. The idea is try to disentangle the controversy between NRP and RM models with the help of simultaneous spectroscopy and photometry.

Narrow-frequency sharp-angular filters using all-dielectric cascaded meta-gratings

Nanophotonics ◽  
2020 ◽  
Vol 9 (10) ◽  
pp. 3443-3450 ◽  
Author(s):  
Wei-Nan Liu ◽  
Rui Chen ◽  
Wei-Yi Shi ◽  
Ke-Bo Zeng ◽  
Fu-Li Zhao ◽  
...  
Keyword(s):  
Thin Film ◽  
Signal To Noise Ratio ◽  
Incident Angle ◽  
Design Strategy ◽  
Transmission Peak ◽  
High Signal ◽  
Waveguide Array ◽  
Signal To Noise ◽  
Center Wavelength ◽  
Noise Ratio

AbstractSelective transmission or filtering always responds to either frequency or incident angle, so as hardly to maximize signal-to-noise ratio in communication, detection and sensing. Here, we propose compact meta-filters of narrow-frequency sharp-angular transmission peak along with broad omnidirectional reflection sidebands, in all-dielectric cascaded subwavelength meta-gratings. The inherent collective resonance of waveguide-array modes and thin film approximation of meta-grating are employed as the design strategy. A unity transmission peak, locating at the incident angle of 44.4° and the center wavelength of 1550 nm, is demonstrated in a silicon meta-filter consisting of two-layer silicon rectangular meta-grating. These findings provide possibilities in cascaded meta-gratings spectroscopic design and alternative utilities for high signal-to-noise ratio applications in focus-free spatial filtering and anti-noise systems in telecommunications.

scholarly journals Low-dose, phase-contrast mammography with high signal-to-noise ratio

2016 ◽  
Vol 7 (2) ◽  
pp. 381 ◽  
Author(s):  
Lukas B. Gromann ◽  
Dirk Bequé ◽  
Kai Scherer ◽  
Konstantin Willer ◽  
Lorenz Birnbacher ◽  
...  
Keyword(s):  
Phase Contrast ◽  
Low Dose ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Signal To Noise ◽  
Noise Ratio
Sign in / Sign up

Export Citation Format

Share Document