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Start Over Subject spectra, optical Content Level Research
1. Identifying multiple populations in M71 using CN
ID:
ivo://CDS.VizieR/J/AJ/159/50
Title:
Identifying multiple populations in M71 using CN
Short Name:
J/AJ/159/50
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have observed their cyanogen CN features at ∼3800 and 4120Å as well as the CH band at ∼4300Å for 145 evolved stars in the Galactic globular cluster M71 using the multi-object spectrograph, Hydra, on the Wisconsin-Indiana-Yale- NOAO-3.5 m telescope. We use these measurements to create two δCN indices finding that both distributions are best fit by two populations: a CN-enhanced and CN-normal. We find that 42%±4% of the red giant branch stars in our sample are CN-enhanced. The percentage of CN-enhanced is 40%±13% for the asymptotic giant branch and 33%±9% for the horizontal branch stars (HB stars), which suggests there are no missing second generation stars at these stages of stellar evolution. The two generations also separate in magnitude and color on the HB, which allows us to find the difference in He abundance between the two populations by fitting appropriate zero-age horizontal branches. The broad range of distances from the cluster's center covered by our sample allows us to study the dependence of the ratio of the number of first to second population stars on the distance from the cluster's center, and we find that this ratio does not vary radially and that the two populations are spatially mixed. Finally, we compare our identification of multiple populations with the classification based on the Na-O anti-correlation and the Hubble Space Telescope UV photometry, and we find good agreement with both methods.
2. WDJ0914+1914 X-Shooter spectrum
ID:
ivo://CDS.VizieR/J/other/Nat/576.61
Title:
WDJ0914+1914 X-Shooter spectrum
Short Name:
J/other/Nat/576.
Date:
21 Oct 2021
Publisher:
CDS
Description:
The detection of a dust disk around the white dwarf star G29-38 and transits from debris orbiting the white dwarf WD 1145+017 confirmed that the photospheric trace metals found in many white dwarfs arise from the accretion of tidally disrupted planetesimals. The composition of these planetesimals is similar to that of rocky bodies in the inner Solar System. Gravitational scattering of planetesimals towards the white dwarf requires the presence of more massive bodies, yet no planet has so far been detected at a white dwarf. Here we report optical spectroscopy of a hot (about 27750 kelvin) white dwarf, WD J091405.30+191412.25, that is accreting from a circumstellar gaseous disk composed of hydrogen, oxygen and sulfur at a rate of about 3.3x10<SUP>9</SUP> grams per second. The composition of this disk is unlike all other known planetary debris around white dwarfs, but resembles predictions for the makeup of deeper atmospheric layers of icy giant planets, with H<SUB>2</SUB>O and H<SUB>2</SUB>S being major constituents. A giant planet orbiting a hot white dwarf with a semi-major axis of around 15 solar radii will undergo substantial evaporation with expected mass loss rates comparable to the accretion rate that we observe onto the white dwarf. The orbit of the planet is most probably the result of gravitational interactions, indicating the presence of additional planets in the system. We infer an occurrence rate of approximately 1 in 10000 for spectroscopically detectable giant planets in close orbits around white dwarfs.