The Star-formation History and Accretion Disk Fraction of the Scorpius-Centaurus OB Association

We present a study of the star-formation history and accretion disk fraction of ~0.6-1.8 Msun stars in the nearest OB Association, Scorpius-Centaurus (Sco-Cen; 10-20 Myr; 100-200 pc). We have performed a low-resolution spectroscopic survey for new, low-mass K- and M-type members of all three subgroups - Upper Scorpius (US), Upper Centaurus-Lupus (UCL) and Lower Centaurus-Crux (LCC). We find that young, pre-main sequence stars have different intrinsic colors for a given spectral type than their main-sequence (MS) counterparts and therefore MS colors and temperatures are unsuitable for de-reddening the low-mass members of Sco-Cen and placing them on an H-R diagram. Using nearby, pre-MS, unreddened moving groups, we derive a spectral type-intrinsic color sequence appropriate for 5-30 Myr old pre-MS stars, and use synthetic spectral energy distribution fits to infer the proper temperature and bolometric correction scale for these young stars. We use this new pre-MS intrinsic color and temperature calibration to place our ~150 newly identified members of Sco-Cen on an H-R diagram. We derive isochronal ages for the B-type MS turn-off and the pre-MS F-type, G-Type members and the K- and M-type members of Sco-Cen. We find a Teff-dependent age trend in the K/M-type stars, similar to previous studies of other nearby star-forming regions. Our F- and G-type isochronal ages for Upper Centaurus-Lupus (UCL; 16±2 Myr;=142 pc) and Lower Centaurus-Crux (LCC; 16±3 Myr; =118 pc) are consistent with previous results. However, our results for Upper Scorpius (US; 10±3 Myr; =145 pc) indicate it is a factor of two older than previously thought. Using ~650 of the pre-MS members of Sco-Cen, we construct an age map, which reveals regions which are systematically younger or older than the mean Sco-Cen age, suggesting that the star-formation history of the three subgroups is more complex than the simple division into three subgroups would imply. Finally, we find a primordial disk fraction for US, UCL and LCC of 9+4-2%, 5+2 -1% and 3+3-1%, respectively, for K-type stars decreasing to <19% (95% CL), 2+5-1%, and 2 +4-1%, respectively, for F-type stars at ~10 Myr, ~16 Myr, and ~16 Myr, respectively

New Young Stars and Brown Dwarfs in the Upper Scorpius Association

To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we have identified candidate members using parallaxes, proper motions, and color-magnitude diagrams from several wide-field imaging surveys and have obtained optical and infrared spectra of several hundred candidates to measure their spectral types and assess their membership. We also have performed spectroscopy on a smaller sample of previously known or suspected members to refine their spectral types and evidence of membership. We have classified 530 targets as members of Upper Sco, 377 of which lack previous spectroscopy. Our new compilation of all known members of the association contains 1631 objects. Although the census of Upper Sco has expanded significantly over the last decade, there remain hundreds of candidates that lack spectroscopy. The precise parallaxes and proper motions from the second data release of Gaia should extend down to substellar masses in Upper Sco, which will greatly facilitate the identification of the undiscovered members.Comment: Astronomical Journal, in press; machine readable tables and fits spectra available at http://personal.psu.edu/kll207/usco.ta

Spaceflight Activates Autophagy Programs and the Proteasome in Mouse Liver

Increased oxidative stress is an unavoidable consequence of exposure to the space environment. Our previous studies showed that mice exposed to space for 13.5 days had decreased glutathione levels, suggesting impairments in oxidative defense. Here we performed unbiased, unsupervised and integrated multi-'omic analysis of metabolomic and transcriptomic datasets from mice flown aboard the Space Shuttle Atlantis. Enrichment analyses of metabolite and gene sets showed significant changes in osmolyte concentrations and pathways related to glycerophospholipid and sphingolipid metabolism, likely consequences of relative dehydration of the spaceflight mice. However, we also found increased enrichment of aminoacyl-tRNA biosynthesis and purine metabolic pathways, concomitant with enrichment of genes associated with autophagy and the ubiquitin-proteasome. When taken together with a down-regulation in NRF2-mediated signaling, our analyses suggest that decreased hepatic oxidative defense may lead to aberrant tRNA post-translational processing, induction of degradation programs and senescence-associated mitochondrial dysfunction in response to the spaceflight environment.

Young Suns Exoplanet Survey: Detection of a wide-orbit planetary-mass companion to a solar-type Sco-Cen member

The Young Suns Exoplanet Survey consists of a homogeneous sample of 70 young, solar-mass stars located in the Lower Centaurus-Crux subgroup of the Scorpius-Centaurus association with an average age of 15 ± 3 Myr. We report the detection of a co-moving companion around the K3IV star TYC 8998-760-1 (2MASSJ13251211–6456207) that is located at a distance of 94.6 ± 0.3 pc using SPHERE/IRDIS on the VLT. Spectroscopic observations with VLT/X-SHOOTER constrain the mass of the star to 1.00±0.02M⊙ and an age of 16.7±1.4 Myr. The companion TYC 8998-760-1 b is detected at a projected separation of 1.71″, which implies a projected physical separation of 162 au. Photometric measurements ranging from Y to M band provide a mass estimate of 14±3 M_(jup) by comparison to BT-Settl and AMES-dusty isochrones, corresponding to a mass ratio of q = 0.013 ± 0.003 with respect to the primary. We rule out additional companions to TYC 8998-760-1 that are more massive than 12 M_(jup) and farther than 12 au away from the host. Future polarimetric and spectroscopic observations of this system with ground and space based observatories will facilitate testing of formation and evolution scenarios shaping the architecture of the circumstellar environment around this ‘young Sun’