GHOST Commissioning Science Results II: a very metal-poor star witnessing the early Galactic assembly

This study focuses on Pristine$\_180956.78$$-$$294759.8$ (hereafter P180956, [Fe/H] $=-1.95\pm0.02$), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph's high efficiency in the blue spectral region ($3700-4800$~\AA) enables the detection of elemental tracers of early supernovae (e.g. Al, Mn, Sr, Eu), which were not accessible in the previous analysis of P180956. The star exhibits chemical signatures resembling those found in ultra-faint dwarf systems, characterised by very low abundances of neutron-capture elements (Sr, Ba, Eu), which are uncommon among stars of comparable metallicity in the Milky Way. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae (\sim10-15\msun), which are needed to reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca] $\sim0.6$), and one fast-rotating intermediate-mass supernova (\sim300\kms, \sim80-120\msun). Both types of supernovae explain the high [Sr/Ba] of P180956 ($\sim1.2$). The small pericentric (\sim0.7\kpc) and apocentric (\sim13\kpc) distances and its orbit confined to the plane (\lesssim 2\kpc), indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to an ultra-faint dwarf galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations.Comment: Submitted to MNRAS. 8 figures, 15page

SPLUS J142445.34-254247.1: An R-Process Enhanced, Actinide-Boost, Extremely Metal-Poor star observed with GHOST

We report on the chemo-dynamical analysis of SPLUS J142445.34-254247.1, an extremely metal-poor halo star enhanced in elements formed by the rapid neutron-capture process. This star was first selected as a metal-poor candidate from its narrow-band S-PLUS photometry and followed up spectroscopically in medium-resolution with Gemini South/GMOS, which confirmed its low-metallicity status. High-resolution spectroscopy was gathered with GHOST at Gemini South, allowing for the determination of chemical abundances for 36 elements, from carbon to thorium. At [Fe/H]=-3.39, SPLUS J1424-2542 is one of the lowest metallicity stars with measured Th and has the highest logeps(Th/Eu) observed to date, making it part of the "actinide-boost" category of r-process enhanced stars. The analysis presented here suggests that the gas cloud from which SPLUS J1424-2542 was formed must have been enriched by at least two progenitor populations. The light-element (Z<=30) abundance pattern is consistent with the yields from a supernova explosion of metal-free stars with 11.3-13.4 Msun, and the heavy-element (Z>=38) abundance pattern can be reproduced by the yields from a neutron star merger (1.66Msun and 1.27Msun) event. A kinematical analysis also reveals that SPLUS J1424-2542 is a low-mass, old halo star with a likely in-situ origin, not associated with any known early merger events in the Milky Way.Comment: 26 pages, 11 figures, accepted for publication on Ap

Imaka:a Lagrange invariant of ELTs

The IMAKA project is a ground layer corrected wide field visible imager proposed for CFHT. It consists of three processes or components: The dome and local turbulence will be controlled by ventilation; the remaining ground layer turbulence will be corrected by a GLAO system and the free atmosphere seeing will be locally reduced by using an Orthogonal Transfer CCD to correct for tip-tilt within the isokinetic angle of field stars. In designing the AO system, whether based on an adaptive secondary mirror or using pupil relay optics, it becomes apparent that the conjugation of the deformable mirror is a difficult constraint to achieve given the large field. It turns out this problem is not isolated to IMAKA, because the Lagrange Invariant for our project is in the same range as that of EAGLE on the E-ELT for example. The effects of tilting the deformable mirror with respect to the pupil or compensating for misconjugation of an adaptive secondary mirror using a tomographic reconstructor have been investigated using Monte-Carlo simulation codes, including our code developed specifically for GLAO simulations. We report on quantitative results from IMAKA simulations for a variety of realistic turbulence conditions for each topical scheme, and allude to how these results are applicable to ELTs' adaptive optics

VLOT : A modest Canadian 20-m telescope

NRC publication: Ye

'Imaka: working towards very wide-field of view AO

Ground-layer adaptive optics (GLAO) has the potential to dramatically increase the efficiency and capabilities of existing ground-based telescopes over a broad range of astronomical science. Recent studies of the optical turbulence above several astronomical sites (e.g. Mauna Kea, Paranal, and Antarctica) show that GLAO can be extended to fields of view of several tens of arcminutes in diameter, larger than previously thought, with angular resolutions close to the free-atmosphere seeing. This is a pivotal result since GLAO science cases benefit from the largest possible corrected fields of view. The corrected areal field of a GLAO system is potentially 2-3 orders of magnitude larger than has been demonstrated to date. The 'Imaka team is working toward an instrument that takes advantage of the one-degree field afforded by Mauna Kea. In this paper we summarize the design/simulation work to date along with our plan to develop an instrument that reaches for this wide field of view. \ua9 2012 SPIE.Peer reviewed: YesNRC publication: Ye

Advantages of Searching for Asteroids from Low Earth Orbit: the NEOSSat Mission

Space-based observatories have several advantages over ground-based observatories in searching for asteroids and comets. In particular, the Aten and Interior to Earth\u2019s Orbit (IEO) asteroid classes may be efficiently sought at low solar elongations along the ecliptic plane. A telescope in low Earth orbit has a sufficiently long orbital baseline to determine the parallax for all Aten and IEO class asteroids discovered with this observing strategy. The Near Earth Object Space Surveillance Satellite (NEOSSat) mission will launch a microsatellite to exploit this observing strategy complementing ground-based search programmes.Peer reviewed: YesNRC publication: Ye

Probing the early Milky Way with GHOST spectra of an extremely metal-poor star in the Galactic disc

Pristine_183.6849 + 04.8619 (P1836849) is an extremely metal-poor ([Fe/H] = -3.3 ± 0.1) star on a prograde orbit confined to the Galactic disc. Such stars are rare and may have their origins in protogalactic fragments that formed the early Milky Way, in low-mass satellites accreted later, or forming in situ in the Galactic plane. Here, we present a chemo-dynamical analysis of the spectral features between 3700-11 000 Å from a high-resolution spectrum taken during Science Verification of the new Gemini High-resolution Optical SpecTrograph. Spectral features for many chemical elements are analysed (Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni), and valuable upper limits are determined for others (C, Na, Sr, Ba). This main sequence star exhibits several rare chemical signatures, including (i) extremely low metallicity for a star in the Galactic disc, (ii) very low abundances of the light α-elements (Na, Mg, Si) compared to other metal-poor stars, and (iii) unusually large abundances of Cr and Mn, where [Cr, Mn/Fe]NLTE &gt; +0.5. A comparison to theoretical yields from supernova models suggests that two low-mass Population III objects (one 10 M· supernova and one 17 M· hypernova) can reproduce the abundance pattern well (reduced χ2 &lt; 1). When this star is compared to other extremely metal-poor stars on quasi-circular, prograde planar orbits, differences in both chemistry and kinematics imply there is little evidence for a common origin. The unique chemistry of P1836849 is discussed in terms of the earliest stages in the formation of the Milky Way.</p

'Imaka: a one-degree high-resolution imager for the Canada-France-Hawaii Telescope

International audienceThe 'Imaka project is a high-resolution wide-field imager proposed for the Canada-France-Hawaii telescope (CFHT) on Mauna Kea. 'Imaka takes advantage of two features of the optical turbulence above Mauna Kea: weak optical turbulence in the free-atmosphere and boundary layer turbulence which is highly confined within a surface layer tens of meters thick and or the telescope enclosures. The combination of the two allows a groundlayer adaptive optics system (GLAO) to routinely deliver an extremely-wide corrected field of view of one-degree at an excellent free-atmosphere seeing limit at visible wavelengths. In addition, populating the focal-plane with orthogonal-transfer CCDs provides a second level of image improvement on the free-atmosphere seeing and the residual GLAO correction. The impact of such an instrument covers a broad range of science and is a natural progression of CFHT's wide-field expertise

Advantages of searching for asteroids from low earth orbit : The NEOSSat mission

NRC publication: Ye

IMAKA: imaging from Mauna KeA with an atmosphere corrected 1 square degree optical imager

International audienceThe goal of this project is to achieve exquisite image quality over the largest possible field of view, with a goal of a FWHM of not more than 0.3" over a square degree field in the optical domain. The narrow PSF will allow detection of fainter sources in reasonable exposure times. The characteristics of the turbulence of Mauna Kea, a very thin ground layer with excellent free seeing allows very wide fields to be corrected by GLAO and would make such an instrument unique. The Ground Layer AO module uses a deformable mirror conjugated to the telescope pupil. Coupled with a high order WFS, it corrects the turbulence common to the entire field. Over such large fields the probability of finding sufficiently numerous and bright natural guide sources is high, but a constellation of laser beacons could be considered to ensure homogeneous and uniform image quality. The free atmosphere seeing then limits the image quality (50% best conditions: 0.2" to 0.4"). This can be further improved by an OTCCD camera, which can correct local image motion on isokinetic scales from residual high altitude tip-tilt. The advantages of the OTCCD are not limited to improving the image quality: a Panstarrs1 clone covers one square degree with 0.1" sampling, in perfect accordance with the scientific requirements. The fast read time (6 seconds for 1.4 Gpixels) also leads to an improvement of the dynamic range of the images. Finally, the guiding capabilities of the OTCCD will provide the overall (local and global) tip-tilt signal