| 1. |
- Olalde, I., et al.
(författare)
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The Beaker phenomenon and the genomic transformation of northwest Europe
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 555:7695, s. 190-196
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Tidskriftsartikel (refereegranskat)abstract
- From around 2750 to 2500 bc, Bell Beaker pottery became widespread across western and central Europe, before it disappeared between 2200 and 1800 bc. The forces that propelled its expansion are a matter of long-standing debate, and there is support for both cultural diffusion and migration having a role in this process. Here we present genome-wide data from 400 Neolithic, Copper Age and Bronze Age Europeans, including 226 individuals associated with Beaker-complex artefacts. We detected limited genetic affinity between Beaker-complex-associated individuals from Iberia and central Europe, and thus exclude migration as an important mechanism of spread between these two regions. However, migration had a key role in the further dissemination of the Beaker complex. We document this phenomenon most clearly in Britain, where the spread of the Beaker complex introduced high levels of steppe-related ancestry and was associated with the replacement of approximately 90% of Britain's gene pool within a few hundred years, continuing the east-to-west expansion that had brought steppe-related ancestry into central and northern Europe over the previous centuries.
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| 2. |
- Bacchus, E., et al.
(författare)
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Project 1640 observations of the white dwarf HD 114174 B
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 469:4, s. 4796-4805
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Tidskriftsartikel (refereegranskat)abstract
- We present the first near infrared spectrum of the faint white dwarf companion HD 114174 B, obtained with Project 1640. Our spectrum, covering the Y, J and H bands, combined with previous TaRgetting bENchmark-objects with Doppler Spectroscopy (TRENDS) photometry measurements, allows us to place further constraints on this companion. We suggest two possible scenarios; either this object is an old, low-mass, cool H atmosphere white dwarf with T-eff similar to 3800 K or a high-mass white dwarf with T-eff > 6000 K, potentially with an associated cool (T-eff similar to 700 K) brown dwarf or debris disc resulting in an infrared excess in the L' band. We also provide an additional astrometry point for 2014 June 12 and use the modelled companion mass combined with the radial velocity and direct imaging data to place constraints on the orbital parameters for this companion.
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| 3. |
- Nilsson, Ricky, et al.
(författare)
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Project 1640 Observations of Brown Dwarf GJ 758 B : Near-infrared Spectrum and Atmospheric Modeling
- 2017
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 838:1
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Tidskriftsartikel (refereegranskat)abstract
- The nearby Sun-like star GJ 758 hosts a cold substellar companion, GJ 758 B, at a projected separation of l less than or similar to 30 au, previously detected in high-contrast multi-band photometric observations. In order to better constrain the companion's physical characteristics, we acquired the first low-resolution (R similar to 50) near-infrared spectrum of it using the high-contrast hyperspectral imaging instrument Project 1640 on Palomar Observatory's 5 m Hale telescope. We obtained simultaneous images in 32 wavelength channels covering the Y, J, and H bands (similar to 9521770 nm), and used data processing techniques based on principal component analysis to efficiently subtract chromatic background speckle-noise. GJ 758 B was detected in four epochs during 2013 and 2014. Basic astrometric measurements confirm its apparent northwest trajectory relative to the primary star, with no clear signs of orbital curvature. Spectra of SpeX/IRTF observed T dwarfs were compared to the combined spectrum of GJ 758 B, with chi(2) minimization suggesting a best fit for spectral type T7.0 +/- 1.0, but with a shallow minimum over T5T8. Fitting of synthetic spectra from the BT-Settl13 model atmospheres gives an effective temperature T-eff = 741 +/- 25 K and surface gravity log g=4.3 +/- 0.5 dex (cgs). Our derived best-fit spectral type and effective temperature from modeling of the low-resolution spectrum suggest a slightly earlier and hotter companion than previous findings from photometric data, but do not rule out current results, and confirm GJ 758 B as one of the coolest sub-stellar companions to a Sun-like star to date.
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| 4. |
- Buntgen, U., et al.
(författare)
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Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.
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| 5. |
- Büntgen, Ulf, et al.
(författare)
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Reply to 'Limited Late Antique cooling'
- 2017
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 10:4, s. 243-243
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 6. |
- Crepp, Justin R., et al.
(författare)
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DIRECT SPECTRUM OF THE BENCHMARK T DWARF HD 19467 B
- 2015
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 798:2
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Tidskriftsartikel (refereegranskat)abstract
- HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar-type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R approximate to 30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5 +/- 1 dwarf with effective temperature T-eff = 978(-43)(+20) K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.
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| 7. |
- Finlator, Kristian, et al.
(författare)
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The minimum halo mass for star formation at z=6-8
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 464:2, s. 1633-1639
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Tidskriftsartikel (refereegranskat)abstract
- Recent analysis of strongly lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV luminosity function of galaxies at z=6-8 rises as a power law down to M-UV=-15, and possibly as faint as-12.5. We use predictions from a cosmological radiation hydrodynamic simulation to map these luminosities on to physical space, constraining the minimum dark matter halo mass and stellar mass that the Frontier Fields probe. While previously published theoretical studies have suggested or assumed that early star formation was suppressed in haloes less massive than 10(9)-10(11) M-circle dot, we find that recent observations demand vigorous star formation in haloes at least as massive as (3.1, 5.6, 10.5) x10(9) M-circle dot at z =(6, 7, 8). Likewise, we find that Frontier Fields observations probe down to stellar masses of (8.1, 18, 32) x10(6) M-circle dot: that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32. Our simulations yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observational constraints on the galaxy-halo connection.
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| 8. |
- Roberts, Lewis C., et al.
(författare)
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CHARACTERIZATION OF THE COMPANION mu HER
- 2016
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 151:6
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Tidskriftsartikel (refereegranskat)abstract
- mu Her is a nearby quadruple system with a G-subgiant primary and several low-mass companions arranged in a 2+2 architecture. While the BC components have been well characterized, the Ab component has been detected astrometrically and with direct imaging but there has been some confusion over its nature, in particular, whether the companion is stellar or substellar. Using near-infrared spectroscopy, we are able to estimate the spectral type of the companion as an M4 +/- 1V star. In addition, we have measured the astrometry of the system for over a decade. We combined the astrometry with archival radial velocity measurements to compute an orbit of the system. From the combined orbit, we are able to compute the mass sum of the system. Using the estimated mass of the primary, we estimate the mass of the secondary as 0.32 MG, which agrees with the estimated spectral type. Our computed orbit is preliminary due to the incomplete orbital phase coverage, but it should be sufficient to predict ephemerides over the next decade.
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| 9. |
- Roberts, Lewis C., et al.
(författare)
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KNOW THE STAR, KNOW THE PLANET. V. CHARACTERIZATION OF THE STELLAR COMPANION TO THE EXOPLANET HOST STAR HD 177830
- 2015
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 150:4
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Tidskriftsartikel (refereegranskat)abstract
- HD 177830 is an evolved K0IV star with two known exoplanets. In addition to the planetary companions it has a late-type stellar companion discovered with adaptive optics imagery. We observed the binary star system with the PHARO near-IR camera and the Project 1640 coronagraph. Using the Project 1640 coronagraph and integral field spectrograph we extracted a spectrum of the stellar companion. This allowed us to determine that the spectral type of the stellar companion is a M4 +/- 1 V. We used both instruments to measure the astrometry of the binary system. Combining these data with published data, we determined that the binary star has a likely period of approximately 800 years with a semimajor axis of 100-200 AU. This implies that the stellar companion has had little or no impact on the dynamics of the exoplanets. The astrometry of the system should continue to be monitored, but due to the slow nature of the system, observations can be made once every 5-10 years.
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