A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbound moving groups, which can be detected kinematically because of their small internal velocity dispersion. The nearby associations have a large extent on the sky, which traditionally has limited astrometric membership determination to bright stars (V 6 mag), with spectral types earlier than ~B5. The Hipparcos measurements allow a major improvement in this situation. Moving groups are identified in the Hipparcos Catalog by combining de Bruijne's refurbished convergent point method with the Spaghetti method of Hoogerwerf & Aguilar. Astrometric members are listed for 12 young stellar groups, out to a distance of ~650 pc. These are the three subgroups Upper Scorpius, Upper Centaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as Vel OB2, Tr 10, Col 121, Per OB2, α Persei (Per OB3), Cas–Tau, Lac OB1, Cep OB2, and a new group in Cepheus, designated as Cep OB6. The selection procedure corrects the list of previously known astrometric and photometric B- and A-type members in these groups and identifies many new members, including a significant number of F stars, as well as evolved stars, e.g., the Wolf-Rayet stars γ2 Vel (WR 11) in Vel OB2 and EZ CMa (WR 6) in Col 121, and the classical Cepheid δ Cep in Cep OB6. Membership probabilities are given for all selected stars. Monte Carlo simulations are used to estimate the expected number of interloper field stars. In the nearest associations, notably in Sco OB2, the later-type members include T Tauri objects and other stars in the final pre–main-sequence phase. This provides a firm link between the classical high-mass stellar content and ongoing low-mass star formation. Detailed studies of these 12 groups, and their relation to the surrounding interstellar medium, will be presented elsewhere. Astrometric evidence for moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, Cam OB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive. OB associations do exist in many of these regions, but they are either at distances beyond ~500 pc where the Hipparcos parallaxes are of limited use, or they have unfavorable kinematics, so that the group proper motion does not distinguish it from the field stars in the Galactic disk. The mean distances of the well-established groups are systematically smaller than the pre-Hipparcos photometric estimates. While part of this may be caused by the improved membership lists, a recalibration of the upper main sequence in the Hertzsprung-Russell diagram may be called for. The mean motions display a systematic pattern, which is discussed in relation to the Gould Belt. Six of the 12 detected moving groups do not appear in the classical list of nearby OB associations. This is sometimes caused by the absence of O stars, but in other cases a previously known open cluster turns out to be (part of) an extended OB association. The number of unbound young stellar groups in the solar neighborhood may be significantly larger than thought previously.

/pdf/a-hipparcos-census-of-the-nearby-ob-associations-44xw838axn.pdf

A Hipparcos Census of the Nearby OB Associations

To date, 204 individual molecular species, comprised of 16 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to seventy, and have been detected across the electromagnetic spectrum from cm-wavelengths to the ultraviolet. This census presents a summary of the first detection of each molecular species, including the observational facility, wavelength range, transitions, and enabling laboratory spectroscopic work, as well as listing tentative and disputed detections. Tables of molecules detected in interstellar ices, external galaxies, protoplanetary disks, and exoplanetary atmospheres are provided. A number of visual representations of this aggregate data are presented and briefly discussed in context.

2018 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

To date, 241 individual molecular species, comprised of 19 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. These molecules range in size from two atoms to seventy, and have been detected across the electromagnetic spectrum from cm-wavelengths to the ultraviolet. This census presents a summary of the first detection of each molecular species, including the observational facility, wavelength range, transitions, and enabling laboratory spectroscopic work, as well as listing tentative and disputed detections. Tables of molecules detected in interstellar ices, external galaxies, protoplanetary disks, and exoplanetary atmospheres are provided. A number of visual representations of this aggregate data are presented and briefly discussed in context. 

2021 Census of Interstellar, Circumstellar, Extragalactic, Protoplanetary Disk, and Exoplanetary Molecules

C1 and C2 carbonaceous chondrites contain several percent of organic matter, mainly as a bridged aromatic polymer containing COOH, OH, and CO groups, as well as heterocyclic rings containing N, O, and S. The remaining 5–30% includes the following compound classes, either present initially or generated by solvolysis: alkanes (mainly normal), alkenes, arenes, alicyclics, alcohols, aliphatic carboxylic acids, purines, pyrimidines, and other basic N-compounds, amino acids, porphyrin-like pigments, carbynes, etc.

Organic compounds in meteorites and their origins

https://iopscience.iop.org/article/10.3847/1538-4365/aae5d2/pdf

Detection of interstellar trans-ethyl alcohol

High-quality J=1$Yields$0 H$sup 12$CN and H$sup 13$CN line profiles at 3.4 mm have been obtained in M17, NGC 2264, Ori A, and NGC 1333. Values for the ratios of the hyperfine-split intensities and the ratio of the integrated intensities of H$sup 12$CN and H$sup 13$CN are given. Collapsing- or expanding- sphere and turbulent-slab cloud models are used to explain the observed line brightness temperatures, the anomalous ratios of the hyperfine-split components, and the abundances of the isotopes. Doppler overlap and Doppler shifting of hyperfine-split components at 1.7 and 1.1 mm are crucial to the results of radiative transport. Comparison of calculations with the data indicates that the parts of the collapsing or the turbulent cloud responsible for observed line widths of greater than 1 or 2 km s$sup -1$ cannot be interacting radiatively via these Doppler effects. No such restrictions are important for the expanding sphere. Conditions of high hydrogen density and moderate HCN column density can be found that are consistent with both CS data and the terrestrial ratio of abundances H$sup 12$CN/H$sup 13$CN, but not with the observed H$sup 13$CN hyperfine-split intensity ratios. An isotope ratio smaller then terrestrial by a factor of 4 or more is required.more » However, parameters remain sufficiently uncertain that further HCN work, especially at shorter wavelengths, is indicated. (AIP)« less

Observations of millimeter-wave HCN in four prototype clouds

than 0.6 percent of total sleep while in the adult chicken and pigeon it comprises 0.3 percent. Hishikawa et al. (2), however, have reported 7.3 ± 1.8 percent REM sleep in young isolated chickens. To our knowledge REM percentages for other avian species have not been reported. We studied in widely separated enclosures two young adult species of diurnal (3) foveate avian predators-a hawk (Buteo jamaicensis arborealis) and a falcon (Herpetotheres cachinnans chapmanni)-for 1 year and for 6 months, respectively. Under Nembutal anesthesia (15 mg/kg), tetrapolar electrodes, 0.5 mm apart and insulated except for the terminal 0.5 mm, were implanted in the cerebral hemispheres 10 mm lateral to the sagittal line. One set was implanted in the hawk, and two sets 7 mm apart in the falcon. Sites of implantation corresponded to the dorsal cortical layer and underlying hyperstriatum (4). Periorbital screw electrodes were implanted to record eye movements [electrooculogram (EOG)]. Two insulated stainless steel wires 1 mm in diameter were placed in the neck muscles to record the electromyogram (EMG). All wires including the ground screw were soldered to a connector affixed to the skull with dental acrylic. The EEG, EOG, and EMG were recorded on an 8-channel polygraph (Grass, model 7). Seven 24-hour recordings were made of the hawk and three 24-hour recordings were made of the falcon. Additionally, 2to 3-hour recordings were made three times a month during nocturnal hours. Two to four weeks of recovery time was needed t after the operations to yield consistent EEG activity. Waking and sleep behavior as well as electrical recordings were similar for both birds. The bird was lightly tethered and could fly a short distance within its cage. During wakefulness the head was elevated, and constant scanning eye movements and spontaneous motor activity were present. The EEG revealed wave frequencies of 10 to 24 hz and an amplitude of 8 to 20 ltv. Occasional slow waves appeared. The EOG showed frequent conjugate as well as disconjugate eye movements. The experimenter's presence consistently evoked an alerting reaction with head and body movements directed toward the source of stimulation. Sleep onset was characterized behaviorally by immobility, eye closure, and abrupt lowering of the head,

https://science.sciencemag.org/content/sci/167/3926/1755.full.pdf

Search for an Effect of the Sun on the Frequency of 18-Centimeter Radiation

Radiofrequency Emission from CH in Comet Kohoutek (1973f)

Molecular studies of two dark nebulae associated with Herbig-Haro objects

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