DOCSLIB.ORG

Observations, Modeling and Theory of Debris Discs

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Observations, Modeling and Theory of Debris Discs Brenda Matthews (HIA, Canada) Geoff Bryden (JPL) Carlos Eiroa (Universidad Autonoma de Madrid) Alexander Krivov (University of Jena) Mark Wyatt (Institute of Astronomy) Physical picture • Debris disks are produced from the remnants of the planet formation process • They are evidence that systems were able to produce at least planetesimal-scale oligarchs (100s of km) • Second generation dust is produced through collisional processes • Debris discs include – Planetesimals (unseen), potentially in narrow “birth rings” – Dust produced from collisions (detected optical centimetre) – All size scales in between 05/28/13 Protostars & Planets VI Courtesy: Zoe Leinhardt Onset of Debris phase 10 Myr Protoplanetary Debris Hernandez et al. 2008, 686, 1195 Dust from 0.1 – 100 AU Dust in belts Massive gas disk No gas Panić et al. 2013, MNRAS, accepted Accretion onto star No accretion (after Wyatt 2008 ARA&A, 46, 339) Optically thick Optically thin 05/28/13 Protostars & Planets VI Detecting Debris Discs Scattered light Thermal emission Shows up subtle structures Highlights larger grains Highlights position of small Can reveal hot/warm/cold grains components Extent of outer disc/halos Can trace the “birth ring” of Does not trace planetesimal planetesimals “birth ring” Resolution has been a Inner region blocked See poster limitation in the past 2B072 (Debes) 05/28/13 Protostars & Planets VI Why we think debris systems could have planets Dust replenished by km- sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric rings Some disks are asymmetric Some systems actually have planets Kalas et al. (2008) Nature / ISAS / JAXA 05/28/13 Protostars & Planets VI Why we think debris systems could have planets Dust replenished by km- Kalas et al. 2008, Science, 322, 1345 sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric, offset rings Some disks are asymmetric Some systems actually have planets Marshall et al. 2011, 05/28/13 Protostars & Planets VI A&A, 529, 117 Why we think debris systems could have planets Dust replenished by km- HD 202628 sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric rings Krist et al. 2002 Some disks are asymmetric Greaves et al. 2013, Some systems actually have in preparation planets 05/28/13 Protostars & Planets VI Why we think debris systems could have planets Dust replenished by km- sized planetesimals Debris disks stirred somehow Cleared inner regions & eccentric rings Some disks are asymmetric Some systems actually have planets Kalas et al. (2008) Heap et al. 2000, ApJ, 539, 435; Golimowski et al. 2006, AJ, 131, 3109; 05/28/13 Protostars & Planets VI Lagrange et al. 2010, Science, 329, 57 3 ways planets interact with discs The orbits of disk particles can be affected by a planet’s gravity in 3 ways: 1. Secular perturbations 2. Resonances 3. Scattering eccentric planet See poster 2B075 (Dawson) inclined planet Movies from Mark Wyatt The challenge: " Debris discs are faint 10-4 Blue: A stars (Su06) Red: FGK stars (E13) Green: FGK stars (T08) 10-5 Purple: AFGKM (M13) 10-6 M K G F A 10-7 Su et al. 2006, ApJ, 653, 675; Eiroa et al. 2013, A&A, in press; Trilling et al. 2008, ApJ, 674, 1086; Matthews et al. 2013, in preparation 05/28/13 Protostars & Planets VI Incidence rates Note that surveys each have their own excess limit that is detectable. It is possible that all stars have discs at some level with many below the detection thresholds. A stars FGK stars M stars 25-35% 3 - 20% Very few! 2.2, 24, 70, 100 um 24, 70, 100/160 um 24, 70, 100, 850 um Chen et al. 2012, ApJ, 756, 133 Carpenter et al. 2009 Gautier et al. 2007 Chen et al. 2011, ApJ, 738, 122 Hillenbrand et al. 2008 Liu et al. 2004 Su et al. 2006, ApJ, 653, 675 Trilling et al. 2008 Lestrade et al. 2006 Absil et al. 2013, Eiroa et al. 2013 Lestrade et al. 2013 Thureau et al. 2013, in prep Sibthorpe et al. 2013, in prep Matthews et al. 2013, in prep Comparable to rate of planets Excellent agreement at all Increasing incidence with wavelengths. aroundwavelength. FGK stars (16%) from Except for very young M stars, Decreases with age. KeplerDecreases with periods with age up toto ~ 85 1Gyr. generally these discs remain days (Fressin et al. 2013) elusive. 05/28/13 Protostars & Planets VI Dust excess evolution • Spitzer studies of the 24 and 70 excesses (Ftot/F*) of A stars found a ∝ t-1 decline in the upper envelope on decay timescale of 150 Myr at 24 µm but longer (~400 Myr) at 70 µm 05/28/13 Protostars & PlanetsRieke VI et al. 2005, Su et al. 2006 Spitzer A star evolution See poster 2B070 (Vican) KB • Luminosity decline relative to the star is evident • 24 micron excess declines fastest (~0 by 400 Myr), suggesting an inside out evolution of the dust (warmer dust is lost first) 05/28/13 Protostars & Planets VI Su et al. 2006 Long term evolution • Steady-state cascade implies that, at any age, disc cannot be dustier than a certain limit • Most discs are consistent with this and are “KBs” • systems with hot dust are not consistent Wyatt et al. 2007; Loehne et al. 2008 with this picture See poster 2B071 (Bonsor) 05/28/13 Protostars & Planets VI Zones of dust distance increases edge-on view of a planetary system temperature decreases planetesimal belt terrestrial planets giant disk halo planets ∼1500 K ∼300 K terrestrial zone ∼150 K ∼50 K See poster 2B074 asteroidal Kuiper-belt (van Lieshout) zone zone wavelength increases 2 µm ∼10 µm ∼24 µm ∼60-70 µm very hot hot warm cold 05/28/13 Protostars & Planets VI Wavelength and Resolution Spitzer SCUBA: Holland et al. 1998, Nature, 392, 788 Spitzer: Stapelfeldt et al. 2004, ApJS, 154, 458 HST: Kalas et al. 2005, Nature, 435, 1067 Herschel: Acke et al. 2012, A&A, 540, 125 ALMA: Boley et al. 2012, ApJ, 750, 21 SCUBA 05/28/13 Protostars & Planets VI Resolved Kuiper Belts • DUNES and DEBRIS both find ~50% detected discs are resolved • wealth of information from resolved images & SEDs • fit Tdust, rdisc, spectral slope • Inclination, position angle • find Ldust/Lstar, Mdisc, rdisc/rblackbody • Dust grain sizes/compositions See posters 2B073 F-star Gamma Dor (Pawellek) (Broekhoven-Fiene et al. 2013) 05/28/132B069 (Schüpper) Protostars & Planets VI Alignment of discs and stars 12 systems have disc and stellar inclinations independently measured (incl. Sun) 1&2$ 34567!! 385--"6!7 2$99$58:* ;<= 385--,0-7 385/">!, 385-00 #$%&'%()& &$*#('%()& Alignment within 10 &)?5@*A 385-7!., 385-/-,-- BC5DAE 9A=<?5-"F5:GG?&% )#<?5-"F5:GG?&% degrees for all systems .+" 2' 0%1 %3'4'' consistent 2' #50 %6' Suggests larger separation -+, planetary inclinations likely to be aligned as -+" well, unlike close-in " /" 0" !" %1#7%1+$%51'5"'' 6%0#'-6!8*!!0/' planets (Brown et al. !""" "+, 2012; Simpson!""!#$%&!'$!()!*+$,*!'-./ et al. ' 2011; Triaud et al. 2010; Winn et al. 2010) "+" Greaves, Eiroa, Matthews et al. in preparation 05/28/13 Protostars & Planets VI Radial distance (AU) 39.4 394. 70µm ) 2 100 10-1 -2 Halos: HR 879910 Data Median Data Surface brightness (mJy/arcsec Model convolved RawRadial Model distance (AU) 1039.4-3 394. 10070µm ) ) 2 • Cold, very extended extensions2 of debris discs, dominated by blow-out1000 grains on hyperbolic or bound orbits10-1 -1 • Planetesimal belt: 100 – 310-2 AU -2 10 Data Median Data Surface brightness (mJy/arcsec Surface brightness (mJy/arcsec Model convolved • Halo: 310 – 2000 AU Raw Model 10-3-3 100160µm 1 10 ) ) 2 2 100 100 100 10-1 (Jy) -1 i -1 10 F 10 10-2 Surface brightness (mJy/arcsec Surface brightness (mJy/arcsec -2 10 -3-2 10 1 10 160µm Radial distance (") ) 153 K 36 K 2 10-3 -1 0 1 2 3 10 10 10 10 10 100 wavelength (!m) λ0 ~ 47 +/- 30 µm β ~ 1.0 +/- 0.1 10-1 05/28/13 Protostars & Planets VI Matthews et al. 2013, in prep Surface brightness (mJy/arcsec 10-2 1 10 Radial distance (") HD 207129 G2V star with no evidence of a halo and no detected planets Evidence of transport of material inward in the disc Disc appears larger with increasing wavelength Marshall et al. A&A 529,A117 (observational) Löhne et al. A&A 537, A110 (detailed modelling) 05/28/13 Protostars & Planets VI Cold disc candidates • Six "cold disk" candidates. These disks have temperatures close to blackbody. • They may be belts of unstirred primordial macroscopic grains that failed to grow to planetesimal sizes. Krivov et al. 2013, ApJ, 772, 32 Eiroa et al. 2011 05/28/13 Protostars & Planets VI Standard model for a debris disc • Radiation pressure blowout • Canonical model of narrow limit “birth ring” • Power law with slope 3-4 • Highly stirred discs produce • Peaks at larger sizes in the case halos of lower stirring (blue curve) • Halos are depressed quickly • Similar effect if there is strong with decreased stirring grain transport (top to bottom) • Strong transport means no halo Krivov05/28/13 et al. 2006; Thebault & AugereauProtostars 2007; & WyattPlanets VI et al. 2011, review chapter & others See posters 2B065 (Ertel) Asteroid belt analogues 2B068 (Kennedy) • Warm dust – Exozodiacal analogs – 1- several AU (habitable zone) ALMA HST 0.6 – mid-IR, Spitzer, IRAS, WISE 870 µm µm • ~1% of stars (or less) in any census • incidence is much lower than for cold dust • component now detectable with ALMA as well Boley et al. 2012; Macgregor et al. 2012 05/28/13 Protostars & Planets VI Warm dust statistics 100 Observed distribution Combined model WISE data can detect -1 m 10 bright exo-Zodis where µ KIN the disk-to-star flux ratio at 12 is better than 0.1 star 10-2 /F disk LBTI will reach 10-3 considerably fainter limits Fraction > F 10-4 Important for target ~Solar System level ~TPF limit LBTI limit WISE limit selection for TPF 10 -4 10 -3 10 -2 10 -1 10 0 10 1 Fdisk/Fstar at 12µm Kennedy & Wyatt 2013 05/28/13 Protostars & Planets VI Vega and Fomalhaut MSX MSX MIPS IRTF IRS PACS PACS IRS ALMA SMA Su et al.
Recommended publications
  • Pushing the Limits of the Coronagraphic Occulters on Hubble Space Telescope/Space Telescope Imaging Spectrograph

    Pushing the Limits of the Coronagraphic Occulters on Hubble Space Telescope/Space Telescope Imaging Spectrograph

    Pushing the limits of the coronagraphic occulters on Hubble Space Telescope/Space Telescope Imaging Spectrograph John H. Debes Bin Ren Glenn Schneider John H. Debes, Bin Ren, Glenn Schneider, “Pushing the limits of the coronagraphic occulters on Hubble Space Telescope/Space Telescope Imaging Spectrograph,” J. Astron. Telesc. Instrum. Syst. 5(3), 035003 (2019), doi: 10.1117/1.JATIS.5.3.035003. Downloaded From: https://www.spiedigitallibrary.org/journals/Journal-of-Astronomical-Telescopes,-Instruments,-and-Systems on 02 Jul 2019 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use Journal of Astronomical Telescopes, Instruments, and Systems 5(3), 035003 (Jul–Sep 2019) Pushing the limits of the coronagraphic occulters on Hubble Space Telescope/Space Telescope Imaging Spectrograph John H. Debes,a,* Bin Ren,b,c and Glenn Schneiderd aSpace Telescope Science Institute, AURA for ESA, Baltimore, Maryland, United States bJohns Hopkins University, Department of Physics and Astronomy, Baltimore, Maryland, United States cJohns Hopkins University, Department of Applied Mathematics and Statistics, Baltimore, Maryland, United States dUniversity of Arizona, Steward Observatory and the Department of Astronomy, Tucson Arizona, United States Abstract. The Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) contains the only currently operating coronagraph in space that is not trained on the Sun. In an era of extreme-adaptive- optics-fed coronagraphs, and with the possibility of future space-based coronagraphs, we re-evaluate the con- trast performance of the STIS CCD camera. The 50CORON aperture consists of a series of occulting wedges and bars, including the recently commissioned BAR5 occulter. We discuss the latest procedures in obtaining high-contrast imaging of circumstellar disks and faint point sources with STIS.
  • Poster Abstracts

    Poster Abstracts

    Aimée Hall • Institute of Astronomy, Cambridge, UK 1 Neptunes in the Noise: Improved Precision in Exoplanet Transit Detection SuperWASP is an established, highly successful ground-based survey that has already discovered over 80 exoplanets around bright stars. It is only with wide-field surveys such as this that we can find planets around the brightest stars, which are best suited for advancing our knowledge of exoplanetary atmospheres. However, complex instrumental systematics have so far limited SuperWASP to primarily finding hot Jupiters around stars fainter than 10th magnitude. By quantifying and accounting for these systematics up front, rather than in the post- processing stage, the photometric noise can be significantly reduced. In this paper, we present our methods and discuss preliminary results from our re-analysis. We show that the improved processing will enable us to find smaller planets around even brighter stars than was previously possible in the SuperWASP data. Such planets could prove invaluable to the community as they would potentially become ideal targets for the studies of exoplanet atmospheres. Alan Jackson • Arizona State University, USA 2 Stop Hitting Yourself: Did Most Terrestrial Impactors Originate from the Terrestrial Planets? Although the asteroid belt is the main source of impactors in the inner solar system today, it contains only 0.0006 Earth mass, or 0.05 Lunar mass. While the asteroid belt would have been much more massive when it formed, it is unlikely to have had greater than 0.5 Lunar mass since the formation of Jupiter and the dissipation of the solar nebula. By comparison, giant impacts onto the terrestrial planets typically release debris equal to several per cent of the planet’s mass.
  • Peter Plavchan

    Peter Plavchan

    Peter Plavchan Assistant Professor of Astronomy Associate Director, George Mason Observatory PI, EarthFinder NASA Mission Concept Study PI, Astrophysics of Exoplanets Instrumentation Lab Co-PI, MINERVA-Australis Department of Physics & Astronomy Office: (703) 903-5893 George Mason University Cell: (626) 234-1628 Planetary Hall 263 Fax: (703) 993-1269 4400 University Dr, MS 3F3 [email protected] Fairfax, VA 22030 http://exo.gmu.edu twitter:@PlavchanPeter Education University of California, Los Angeles, Los Angeles, CA 2001-2006 MS, PhD in Physics California Institute of Technology, Pasadena, CA 1996-2001 BS in Physics, with honor Awards & Honors College of Science Excellence in Mentoring award nomination 2019 College of Natural and Applied Sciences Research Award, MSU 2017 NASA Group Achievement Award 2017 Citation: For the development and tests at Mauna Kea observatories of a near-infrared Laser Frequency Comb as a wavelength standard for the detection and characterization of exoplanets. NASA Honor Achievement Award, NASA Exoplanet Archive Team 2014 Citation: For outstanding achievement in the rapid and on-budget launch of the NASA Exoplanet Archive NASA Honor Achievement Award, Spitzer Science In-Reach Team 2010 Citation: For outstanding support of Spitzer IRAC Warm Instrument Characterization and significant contributions to NASA and JPL commitments to education of the global community. UCLA Physics Division Fellowship 2001-2006 Kobe International School of Planetary Sciences Fellowship 2005 Astronomy Department Outstanding Teaching
  • New Metallicity Calibration Down to [Fe/H]=−2.75

    New Metallicity Calibration Down to [Fe/H]=−2.75

    CSIRO PUBLISHING www.publish.csiro.au/journals/pasa Publications of the Astronomical Society of Australia, 2003, 20, 165–172 New Metallicity Calibration Down to [Fe/H] =−2.75 dex S. Karaali, S. Bilir, Y. Karata¸sand S. G. Ak Department of Astronomy and Space Sciences, Science Faculty, Istanbul University, 34452 Istanbul, Turkey [email protected] Received 2002 August 29, accepted 2003 February 1 Abstract: We have taken 88 dwarfs, covering the colour-index interval 0.37 ≤ (B−V)0 ≤ 1.07 mag, with metallicities −2.70 ≤ [Fe/H] ≤+0.26 dex, from three different sources for new metallicity calibration. The catalogue of Cayrel de Strobel et al. (2001), which includes 65% of the stars in our sample, supplies detailed information on abundances for stars with determination based on high-resolution spectroscopy. In constructing the new calibration we have used as ‘corner stones’ 77 stars which supply at least one of the following conditions: (i) the parallax is larger than 10 mas (distance relative to the Sun less than 100 pc) and the galactic latitude is absolutely higher than 30◦; (ii) the parallax is rather large, if the galactic latitude is absolutely low and vice versa. Contrary to previous investigations, a third-degree polynomial is fitted for the new calibration: [Fe/H] = 0.10 − 2.76δ − 24.04δ2 + 30.00δ3. The coefficients were evaluated by the least-squares method, without regard to the metallicity of Hyades. However, the constant term is in the range of metallicity determined for this cluster, i.e. 0.08 ≤ [Fe/H] ≤ 0.11 dex. The mean deviation and the mean error in our work are equal to those of Carney (1979), for [Fe/H] ≥−1.75 dex where Carney’s calibration is valid Keywords: stars: abundances — stars: metallicity calibration — stars: metal-poor 1 Introduction recent analyses (Rosenberg et al.
  • Research at the Belgrade Astronomical Observatory

    Research at the Belgrade Astronomical Observatory

    ASTRONOMY AND SPACE SCIENCE eds. M.K. Tsvetkov, L.G. Filipov, M.S. Dimitrijevic,´ L.C.ˇ Popovic,´ Heron Press Ltd, Sofia 2007 Influence of Collisional Processes on the Astrophysical Plasma Spectra – Research at the Belgrade Astronomical Observatory M.S. Dimitrijevic´ Astronomical Observatory, Volgina 7, 11160 Belgrade, Serbia Abstract. Activities on the project “Influence of collisional processes on the astrophysical plasma spectra”, supported by the Ministry of Science and Envi- ronment protection from 1st January 2002 up to 31st December 2005 are re- viewed, including other scientific results of the project participants. 1 Research on the Influence of Collisional Processes on the Astro- physical Plasma Spectra on Belgrade Astronomical Observatory From 1. January 2002, activities on investigation of the influence of collisional processes on the astrophysical plasma spectra are organized at Belgrade astronomical observatory within the frame of the project with the same name, supported by the Ministry of Science and Environment protection of Serbia. Investigations made within the frame of the Project concern plasma in astrophysics, lab- oratory and technology and the corresponding modelling, determination and research of atomic and molecular processes, optical properties and spectra, with a particular accent on the role of collisional processes. The particular attention has been paid to the inves- tigation of spectral line profiles, broadened by collisions with charged particles (Stark effect). Such investigations are of interest for the diagnostics and modelling of stellar plasma, plasma in laboratory and technological plasma. Semiclasical perturbation and Modified semiempirical methods were used, tested and investigated. Stark broadening parameters, line width and shift, were determined for a large number of spectral lines of Ag I, Ar I, Cd I, Ga I, Ge I, Kr I, Ne I, F II, In II, Ne II, Ti II, Be III, Cd III, Co III, Cu III, F III, S III, Si III, Zn III, and Si IV.
  • Flares on Active M-Type Stars Observed with XMM-Newton and Chandra

    Flares on Active M-Type Stars Observed with XMM-Newton and Chandra

    Flares on active M-type stars observed with XMM-Newton and Chandra Urmila Mitra Kraev Mullard Space Science Laboratory Department of Space and Climate Physics University College London A thesis submitted to the University of London for the degree of Doctor of Philosophy I, Urmila Mitra Kraev, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Abstract M-type red dwarfs are among the most active stars. Their light curves display random variability of rapid increase and gradual decrease in emission. It is believed that these large energy events, or flares, are the manifestation of the permanently reforming magnetic field of the stellar atmosphere. Stellar coronal flares are observed in the radio, optical, ultraviolet and X-rays. With the new generation of X-ray telescopes, XMM-Newton and Chandra , it has become possible to study these flares in much greater detail than ever before. This thesis focuses on three core issues about flares: (i) how their X-ray emission is correlated with the ultraviolet, (ii) using an oscillation to determine the loop length and the magnetic field strength of a particular flare, and (iii) investigating the change of density sensitive lines during flares using high-resolution X-ray spectra. (i) It is known that flare emission in different wavebands often correlate in time. However, here is the first time where data is presented which shows a correlation between emission from two different wavebands (soft X-rays and ultraviolet) over various sized flares and from five stars, which supports that the flare process is governed by common physical parameters scaling over a large range.
  • 121012-AAS-221 Program-14-ALL, Page 253 @ Preflight

    121012-AAS-221 Program-14-ALL, Page 253 @ Preflight

    221ST MEETING OF THE AMERICAN ASTRONOMICAL SOCIETY 6-10 January 2013 LONG BEACH, CALIFORNIA Scientific sessions will be held at the: Long Beach Convention Center 300 E. Ocean Blvd. COUNCIL.......................... 2 Long Beach, CA 90802 AAS Paper Sorters EXHIBITORS..................... 4 Aubra Anthony ATTENDEE Alan Boss SERVICES.......................... 9 Blaise Canzian Joanna Corby SCHEDULE.....................12 Rupert Croft Shantanu Desai SATURDAY.....................28 Rick Fienberg Bernhard Fleck SUNDAY..........................30 Erika Grundstrom Nimish P. Hathi MONDAY........................37 Ann Hornschemeier Suzanne H. Jacoby TUESDAY........................98 Bethany Johns Sebastien Lepine WEDNESDAY.............. 158 Katharina Lodders Kevin Marvel THURSDAY.................. 213 Karen Masters Bryan Miller AUTHOR INDEX ........ 245 Nancy Morrison Judit Ries Michael Rutkowski Allyn Smith Joe Tenn Session Numbering Key 100’s Monday 200’s Tuesday 300’s Wednesday 400’s Thursday Sessions are numbered in the Program Book by day and time. Changes after 27 November 2012 are included only in the online program materials. 1 AAS Officers & Councilors Officers Councilors President (2012-2014) (2009-2012) David J. Helfand Quest Univ. Canada Edward F. Guinan Villanova Univ. [email protected] [email protected] PAST President (2012-2013) Patricia Knezek NOAO/WIYN Observatory Debra Elmegreen Vassar College [email protected] [email protected] Robert Mathieu Univ. of Wisconsin Vice President (2009-2015) [email protected] Paula Szkody University of Washington [email protected] (2011-2014) Bruce Balick Univ. of Washington Vice-President (2010-2013) [email protected] Nicholas B. Suntzeff Texas A&M Univ. suntzeff@aas.org Eileen D. Friel Boston Univ. [email protected] Vice President (2011-2014) Edward B. Churchwell Univ. of Wisconsin Angela Speck Univ. of Missouri [email protected] [email protected] Treasurer (2011-2014) (2012-2015) Hervey (Peter) Stockman STScI Nancy S.
  • Chromospherically Young, Kinematically Old Stars

    Chromospherically Young, Kinematically Old Stars

    A&A 384, 912–924 (2002) Astronomy DOI: 10.1051/0004-6361:20011815 & c ESO 2002 Astrophysics Chromospherically young, kinematically old stars H. J. Rocha-Pinto1,3,B.V.Castilho2, and W. J. Maciel1 1 Instituto Astronˆomico e Geof´ısico (USP), Av. Miguel Stefano 4200, 04301-904 S˜ao Paulo SP, Brazil e-mail: [email protected] 2 Laborat´orio Nacional de Astrof´ısica, CP 21, 37500-000 Itajub´a MG, Brazil e-mail: [email protected] 3 Depart. of Astronomy, University of Virginia, Charlottesville, VA 22903, USA e-mail: [email protected] Received 3 July 2001 / Accepted 18 December 2001 Abstract. We have investigated a group of stars known to have low chromospheric ages, but high kinematical ages. Isochrone, chemical and lithium ages are estimated for them. The majority of stars in this group show lithium abundances much smaller than expected for their chromospheric ages, which is interpreted as an indication of their old age. Radial velocity measurements in the literature also show that they are not close binaries. The results suggest that they can be formed from the coalescence of short-period binaries. Coalescence rates, calculated taking into account several observational data and a maximum theoretical time scale for contact, in a short-period pair, predict a number of coalesced stars similar to what we have found in the solar neighbourhood. Key words. stars: late-type – stars: chromospheres – Galaxy: evolution 1. Introduction investigate the chromospheric activity in single stars. Due to this, the division of these surveys into two classes, of The chromospheric activity of a late-type star is frequently active and inactive stars, corresponds closely to an age interpreted as a sign of its youth.
  • Download This Article in PDF Format

    Download This Article in PDF Format

    A&A 609, A8 (2018) Astronomy DOI: 10.1051/0004-6361/201731453 & c ESO 2017 Astrophysics The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release? C. A. L. Bailer-Jones Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany e-mail: [email protected] Received 27 June 2017 / Accepted 12 August 2017 ABSTRACT I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which pass within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars with large radial velocity uncertainties (>10 km s−1), and partly because of missing stars in GDR1 (especially at the bright end). The closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function of the time and distance of closest approach.
  • Observations and Modelling of a Large Optical Flare on at Microscopii

    Observations and Modelling of a Large Optical Flare on at Microscopii

    A&A 383, 548–557 (2002) Astronomy DOI: 10.1051/0004-6361:20011743 & c ESO 2002 Astrophysics Observations and modelling of a large optical flare on AT Microscopii D. Garc´ıa-Alvarez1, D. Jevremovi´c1,2,J.G.Doyle1, and C. J. Butler1 1 Armagh Observatory, College Hill, Armagh BT61 9DG N. Ireland e-mail: [email protected], [email protected], [email protected] 2 Astronomical Observatory, Volgina 7, 11070 Belgrade, Yugoslavia Received 26 September 2001 / Accepted 5 December 2001 Abstract. Spectroscopic observations covering the wavelength range 3600–4600 A˚ are presented for a large flare on the late type M dwarf AT Mic (dM4.5e). A procedure to estimate the physical parameters of the flaring plasma has been used which assumes a simplified slab model of the flare based on a comparison of observed and computed Balmer decrements. With this procedure we have determined the electron density, electron temperature, optical thickness and temperature of the underlying source for the impulsive and gradual phases of the flare. The magnitude and duration of the flare allows us to trace the physical parameters of the response of the lower atmosphere. In order to check our derived values we have compared them with other methods. In addition, we have also applied our procedure to a stellar and a solar flare for which parameters have been obtained using other techniques. Key words. stars: activity – stars: chromospheres – stars: flare – stars: late-type 1. Introduction (Doyle & Mathioudakis 1990; Byrne & McKay 1990). Even more energetic flares occur on the RS CVn binary Stellar flares are events where a large amount of energy is systems, the total flare energy in the largest of this type released in a short interval of time, radiating at almost of systems may exceed E ∼ 1038 erg (Doyle et al.
  • 1 the Effect of a Strong Stellar Flare on the Atmospheric Chemistry of An

    1 the Effect of a Strong Stellar Flare on the Atmospheric Chemistry of An

    The Effect of a Strong Stellar Flare on the Atmospheric Chemistry of an Earth-like Planet Orbiting an M dwarf (Astrobiology, accepted) Antígona Segura 1,* , Lucianne Walkowicz 2,* , Victoria Meadows 3,* , James Kasting 4,* , Suzanne Hawley 5 1Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 2University of California at Berkeley, 3University of Washington, 4Pennsylvania State University, 5University of Washington *Members of the Virtual Planet Laboratory Lead Team of the NASA Astrobiology Institute. To whom correspondence should be directed: Antígona Segura Universidad Nacional Autónoma de México Instituto de Ciencias Nucleares Circuito Exterior C.U. A.Postal 70-543 04510 México D.F. Phone: 52 (55) 5622 4739 ext. 269 Fax 52 (55) 56 22 46 82 E-mail: [email protected] Running title: Flare effect on an Earth-like planet Abstract Main sequence M stars pose an interesting problem for astrobiology: their abundance in our galaxy makes them likely targets in the hunt for habitable planets, but their strong chromospheric activity produces high energy radiation and charged particles that may be detrimental to life. We studied the impact of the 1985 April 12 flare from the M dwarf, AD Leonis (AD Leo), simulating the effects from both UV radiation and protons on the atmospheric chemistry of a hypothetical, Earth-like planet located within its habitable zone. Based on observations of solar proton events and the Neupert effect we estimated a proton flux associated with the flare of 5.9×10 8 protons cm -2 sr -1 s -1 for particles with energies >10MeV. Then we calculated the abundance of nitrogen oxides produced by the flare by scaling the production of these compounds during a large solar proton event called the “Carrington event”.
  • Bibliography from ADS File: Doyle.Bib June 27, 2021 1

    Bibliography from ADS File: Doyle.Bib June 27, 2021 1

    Bibliography from ADS file: doyle.bib Nelson, C. J., Doyle, J. G., & Erdélyi, R., “On the relationship between magnetic August 16, 2021 cancellation and UV burst formation”, 2016MNRAS.463.2190N ADS Hill, A., Byrnes, P., Fitzsimmons, J., et al., “A prototype of the NFIRAOS to instrument thermo-mechanical interface”, 2016SPIE.9912E..02H ADS Murphy, T., Kaplan, D. L., Stewart, A. J., et al., “The ASKAP Variables and Reid, A., Mathioudakis, M., Doyle, J. G., et al., “Magnetic Flux Cancellation in Slow Transients (VAST) Pilot Survey”, 2021arXiv210806039M ADS Ellerman Bombs”, 2016ApJ...823..110R ADS Vilangot Nhalil, N., Nelson, C. J., Mathioudakis, M., Doyle, J. G., & Ramsay, Shetye, J., Doyle, J. G., Scullion, E., et al., “High-cadence observations of G., “Power-law energy distributions of small-scale impulsive events on the spicular-type events on the Sun”, 2016A&A...589A...3S ADS active Sun: results from IRIS”, 2020MNRAS.499.1385V ADS Wedemeyer, S., Bastian, T., Brajša, R., et al., “Solar Science with the At- Ramsay, G., Doyle, J. G., & Doyle, L., “TESS observations of southern ultrafast acama Large Millimeter/Submillimeter Array-A New View of Our Sun”, rotating low-mass stars”, 2020MNRAS.497.2320R ADS 2016SSRv..200....1W ADS Doyle, L., Ramsay, G., & Doyle, J. G., “Superflares and variability in solar- Shetye, J., Doyle, J. G., Scullion, E., Nelson, C. J., & Kuridze, D., “High Ca- type stars with TESS in the Southern hemisphere”, 2020MNRAS.494.3596D dence Observations and Analysis of Spicular-type Events Using CRISP On- ADS board SST”, 2016ASPC..504..115S ADS Srivastava, A. K., Rao, Y. K., Konkol, P., et al., “Velocity Response of the Ob- Park, S.