Presentation on theme: "SPECTROSCOPY OVERVIEW The Science Case: High Resolution Spectroscopy of (cool) stars Basic tools for specifications and verification One example of similar."— Presentation transcript:
SPECTROSCOPY OVERVIEW The Science Case: High Resolution Spectroscopy of (cool) stars Basic tools for specifications and verification One example of similar design and different implementations: UVES, FEROS, HARPS Successful Program: VLT instrumentation Aspects of Optical design (B. Delabre) L. Pasquini July 2002 This cycle is directed to ASTRONOMERS Develops through a logical path which goes from conception to construction and operations of the instrument
SPECTROSCOPY Science Cases L. Pasquini July 2002 Science cases: Why do we want to have a new instrument ? Which science to address? Which Outstanding problems to solve ? How ? Which Telescope ? Which fraction of the time is available ? Related questions: Which community will serve ? What is already available to them ? What is the state of art ? The competition ? The alternatives? Some Practical Aspects: Feasibility, Financial, Timescale
SPECTROSCOPY WHY H-R Spectroscopy ? L. Pasquini July 2002 Spectroscopy brings the largest amount of information. The best (and in some case unique) way of making physics. From Zoccali et al. 2002, search for CN - CH variations in Globular Clusters
SPECTROSCOPY Cool Stars: Some Topics L. Pasquini July 2002 Detailed Chemical Abundance: Distance Scale, Stellar Populations, Star Formation History, Chemical Evolution, Age of the Galaxy Primordial Nucleosynthesis: Li, Be abundance Stellar Interior: Diffusion, Mixing, oscillations.. Accurate Radial velocities : Dynamics of complex systems, Binaries, Exo- Planets, short and long term variations Rotation & magnetic fields: Activity, Dynamo, Solar-stellar connection, Angular Momentum evolution...
The chemical evolution of Globular Clusters: some unexpected (?) results with VLT ESO Large Programme, PI: Raffaele Gratton (PD)
Content - Distances to globular clusters and impact on ages: short and long distance scales - Star-to-star chemical inhomogeneities: the Na-O anticorrelation - Lithium abundances - ESO Large Program 165-L0263
Distances to globular clusters and impact on ages: short and long distance scales
Comparison between confidence range for globular clusters ages and values allowed by Universe geometry
True distance modulus to the LMC according various methods
Globular cluster distances from Main-Sequence fitting to local subdwarfs
Systematic effects and total error budget associated with the MS fitting distances to Globular Clusters Effect (m-M) Malmquist bias negligible Lutz-Kelker correction 0.02 Binaries (in the field) 0.02 Binaries (in clusters) 0.03 Photometric calibrations (0.01 mag) 0.04 Reddening scale (0.015 mag) 0.07 Metallicity scale (0.1 dex) 0.08 Total uncertainty (1 ) 0.12 Reddening free T eff calibration
Star-to-star chemical inhomogeneities: the Na-O anticorrelation
Variations among MS stars in 47 Tuc (Briley et al. 1994) Variations in the strength of CH and CN bands Noticed since early seventies (Osborn 1971) from DDO photometry and spectroscopy Bimodal distribution along the RGB (Norris & Smith 1980s) NGC6752
Kraft, Sneden and coworkers: The O-Na anticorrelation for giants in globular clusters
Presence of elements processed through the complete CNO-cycle. At these temperatures 22 Ne+p 23 Na (Denissenkov & Denissenkova 1990; Langer & Hoffman 1995; Cavallo et al. 1996). At higher temperatures, also 26 Mg+p 27 Al From Langer et al. 1993
A first mixing episode occurs at the base of the RGB, due to the inward penetration of the outer convective envelope in regions where some H-burning (through uncomplete CN-cycle) occurred during the latest phases of MS evolution (first dredge-up: Iben 1964). First dredge up causes only minor effect in metal-poor stars At the same phases, dilution (by a factor of ~20) of the surface Li abundance occurs Mixing episodes along the RGB evolution of small mass stars
The maximum inward penetration of the outer convective envelope at the base of the RGB creates a discontinuity in molecular weight ( -barrier) that prevents further mixing, until is canceled by the outward expansion of the H-burning shell (RGB clump) (Sweigart & Mengel 1979; Charbonnel 1994). Further mixing (due e.g. to meridional circulations activated by core rotation is possible only after the RGB clump Role of the molecular weight barrier
Molecular weight-barrier along the RGB (from Charbonnel et al. 1998)
Field stars conform this theoretical paradigma (Gratton et al. 2000) However abundances of O and Na are not affected: mixing is not deep enough to reach regions where complete CNO cycle occurs
There is a systematic difference between field and cluster stars. Important: this might be correlated with the 2nd parameter effect - Systematic different core-rotation core and total mass at He-flash - Mixing of He It may also affect HB magnitudes (and then distance scales) Possible hints for a correlation between the 2nd parameter and the Na-O anticorrelation may be suggested by these graphs by Carretta et al. (1996)
What is going on in cluster stars? There are mainly two scenarios: - Deep mixing episodes: may only occur along the RGB, after the clump (temperature is not large enough in TO-stars) - Accretion: should be present independent of the evolutionary phase (the material comes from now extincted TP AGB stars, undergoing hot bottom burning). Accretion might occur:. on protostars (Cottrell & Da Costa). on already formed stars (D’Antona, Gratton & Chieffi) Not distinguishable from observations of bright giants Observations of stars fainter than the clump
and primordial nucleosynthesis (figure from Suzuki et al. 2000)
Lithium abundances from halo stars on the Spite’s paletau (data from Suzuki et al. 2000)
Main concern: Surface Li depletion due to sedimentation due to some mixing (figure from Vauclair & Charbonnel 1998)
Role of globular clusters We may compare abundances in TO and subgiants looking for costraints about sedimentation: - comparing abundances in TO-stars and subgiants effects of sedimentation should be canceled when the outer convective envelope penetrates inward (dilution is independent of diffusion) - elements other than Li provide costraints on effects of sedimentation Comparison between abundances for TO-stars and subgiants
Previous observations of Li in globular clusters (figure from Charbonnel et al. 2000) Field stars GC stars: filled symbols: Deliyannis et al. open symbols: Pasquini & Molaro Castilho et al.
Previous observations of Li in globular clusters Li abundances in NGC6397 stars from Castilho et al. (2000)
PI: R. Gratton co-authors: P. Bonifacio, A. Bragaglia, E. Carretta, V. Castellani, M. Centurion, A. Chieffi, R. Claudi, G. Clementini, F. D’Antona, S. Desidera, P. Francois, F. Grundhal, S. Lucatello, P. Molaro, L. Pasquini, C. Sneden, M. Spite, F. Spite, O. Straniero VLT2 (Kueyen)+UVES 12 nights in June and September nights in August and October 2001 ESO Large Program 165-L0263: Distances, Ages and Metal Abundances in Globular Cluster Dwarfs
Clusters selected for observations The closest globular clusters (but M4 for which differential reddening is important) cluster V(TO) [Fe/H] NGC NGC Tuc
NGC 6397 and NGC Stars selected for observations: 14 TO stars and 12 subgiants (below the RGB clump) in NGC6397 and NGC6752
47 Tucanae - Stars selected for observations: 3 TO stars and 8 subgiants (below the RGB clump)
Field star sample: 34 metal-poor stars with good parallaxes from the Hipparcos satellite Green points: single stars Red squares: binaries
Our spectra have R~40,000, and S/N~ for stars in NGC6397, S/N~20-60 for stars in NGC 6752 and 47 Tucanae.. The spectral range is Å. We show the correlation between EWs measured with an authomatic procedure on spectra of two TO stars in NGC6752 (upper panel) and NGC6397 (lower panel) Typical errors are 3 mÅ for stars in NGC 6397, and 5 mÅ for stars in NGC 6752 and 47 Tucanae Accurate EWs can be derived from our spectra
T eff ’s from spectra: - Balmer line profiles Analysis procedure strictly identical for field and cluster stars Reddening free
Comparison between T eff ’s from H and from colours (calibration by Kurucz, model without overshooting) Green points: single stars Red squares: binaries Mean offset: -68 27 K r.m.s.=159 K Reddening zero point error: E(B-V)=0.008
Our T eff scale agrees quite well with that of Alonso et al. based on the IRFM Average difference is T(Us)-T(A)=29 12 K (r.m.s.= 78 K, 42 stars) Eliminating five outliers: T(Us)-T(A)=0.906T(A) +564 K (r.m.s.= 35 K, 37 stars)
Results Impact of microscopic diffusion on models of low mass stars The O-Na anticorrelation among globular cluster TO-stars Lithium abundances in TO-stars and subgiants of globular clusters Distances and Ages of Globular Clusters Comparison between abundances in GC and field stars Rotation of TO-stars in globular clusters
Impact of microscopic diffusion on models of low mass stars
Microscopic diffusion is a basic physical mechanism, that should be included in stellar models It causes sedimentation of heavy elements, mainly He; in low mass (M~0.8 M 0 ), metal-poor ([Fe/H] -2) stars near the TO, also O and Fe are expected to be depleted significantly The net effects of sedimentation are: - ages are reduced by about 10% - Li abundances may be significantly reduced with respect to the original value Our observations of TO and subgiants in NGC6397 (M~0.8 M 0, [Fe/H]=-2.0) allow to costrain sedimentation effects
Abundances in stars of NGC6397 Star S/N [Fe/H] [O/Fe] TO-stars <> 0.01 Subgiants < <> 0.03
Prediction of models with microscopic diffusion (0.8 M o ) Model [Fe/H] TO-subgiants Castellani et al for [Fe/H]= -2.0 Salasnich et al for [Fe/H]= for [Fe/H]= -2.3 Chieffi & Straniero for [Fe/H]= -2.3 NGC 0.04 for [Fe/H]= -2.0 Conclusion: Models predict much larger sedimentation due to microscopic diffusion than actually observed. There should be some mechanism that prevents sedimentation
The O-Na anticorrelation among globular cluster stars
There are mainly two scenarios: - Deep mixing episodes: may only occur along the RGB (temperature is not large enough in TO-stars) - Pollution: should be present independent of the evolutionary phase (the material comes from now extincted TP AGB stars, undergoing hot bottom burning). Pollution might occur:. on protostars (Cottrell & Da Costa). on already formed stars (D’Antona, Gratton & Chieffi) Our observations of TO-stars in NGC6752 (a cluster which exhibits a clear O-Na among giants) allows to make a definitive test on the deep mixing scenarios
Na doublet at Å in TO-stars of NGC6752 (these stars have virtually identical atmospheric parameters) There is a clear star-to-star variation in Na abundances
OI triplet at Å in TO-stars of NGC6752. These stars have virtually identical atmospheric parameters. There is a clear star-to-star variation in O-abundances, anticorrelated with variations in Na abundances
The O-Na anticorrelation among stars in NGC6752. Filled squares: TO stars Empty squares: subgiants. The observed anticorrelation is very similar to that observed in giants
The correlation between the Strömgren c 1 index and the Na abundance among stars in NGC6752. Filled squares: TO stars Empty squares: subgiants The c 1 index is correlated with Na abundances among subgiants.
The Mg-Al anticorrelation among stars in NGC6752. Upper panel: TO stars Lower panel: subgiants. Na rich stars are Al-rich and Mg-poor. This is most clear among subgiants.
C-N anticorrelation in subgiants of NGC6752 CN-band at 3883 ÅG-band Stars are ordered according to increasing Na abundance [N/Fe]=1.0 [N/Fe]=1.1 [N/Fe]=1.3 [N/Fe]=0.0 [N/Fe]=1.2 [N/Fe]=1.3 [N/Fe]=1.2 [N/Fe]=1.45 [N/Fe]=1.5 [C/Fe]=-0.05 [C/Fe]=-0.40 [C/Fe]=-0.15 [C/Fe]=-0.35 [C/Fe]=-0.65 [C/Fe]=-0.60 [C/Fe]=-0.25 [C/Fe]=-0.35
C and N abundances in NGC6752 subgiants [(C+N)/Fe]=0 All O transformed into N
C and N abundances in subgiants of NGC6397 [N/Fe]=1.4 [N/Fe]=1.3 [N/Fe]=1.5 [C/Fe]=+0.05 [C/Fe]=-0.10 [C/Fe]=0.0 Very high N abundance ! [O/Fe]=+0.21 0.05 but [(C+N+O)/Fe]=+0.58 0.10
Conclusions: The O-Na anticorrelation is present among TO-stars and subgiants in NGC6752. For the same stars, also a Mg-Al anticorrelation is observed This clearly rules out deep mixing as explanation for the O-Na anticorrelation The sum of C+N abundances is not constant: a substantial fraction of O is transformed into N in some NGC6752 stars N is overabundant by a large factor in subgiants of NGC6397: while O is almost solar, the sum of C+N+O is overabundant as in halo field stars
Lithium abundances in TO-stars and subgiants of globular clusters
Li doublet in TO-stars of NGC6397 Line strength is the same in all stars
Average Li abundance: log n(Li)=2.34 r.m.s=0.056 dex Maximum intrinsic scatter dex This is to be fulfilled by stellar models which predict Li depletion. If this is primordial Li then the baryonic density is: b h 2 =0.016 or b h 2 =0.005 0.002
Li abundances in field and (Na-poor) cluster stars. They occupy the same location Dilution factor is about 15 for both field (Gratton et al. 2000) and cluster stars, in agreement with theoretical predictions Spite’s plateau
Lithium abundances and primordial nucleosynthesis (figure from Suzuki et al. 2000)
Li doublet in TO-stars of NGC6752 There are clear star-to-star variations EW=18.5 mÅ EW= 5.9 mÅ EW=15.7 mÅ EW=19.5 mÅ EW=17.0 mÅ EW=18.5 mÅ EW=28.2 mÅ EW=32.9 mÅ EW=33.2 mÅ
Na-Li anticorrelation for TO stars in NGC6752 Li is anticorrelated with Na in TO-stars of NGC6752; however some Li is observed also in most Na-rich, O-poor stars Field star value
How it is possible that some Li is observed also when products of complete CNO-burning are observed? This is possible in accretion scenarios since there are phases in which massive TP-AGB stars produce Li and other where they destroy Li (Ventura et al. 2001)
Conclusions: Stars at the TO of NGC6397, and O-rich TO-stars in NGC6752 have Li abundances very close to those of stars on the Spite’s plateau Na-rich, O-poor TO-stars in NGC6752 have Li abundances lower than that of stars on the Spite’s plateau, but some Li is still observed The observed dilution factor for subgiants is similar to that predict by current models
Distances and Ages of Globular Clusters
Colour of the main sequence at M V =6 Line is not best fit, but the prediction of models by Chieffi & Straniero
Reddenings toward NGC6397, NGC6752 and 47 Tuc Comparing the Teff-colour relations for field and cluster stars: Source E(B-V) NGC 6397 E(B-V) NGC6752 E(B-V) 47Tuc (b-y) (B-V) average Harris Schlegel maps
Main sequence fitting distance to NGC6397 and NGC6752 NGC6397 NGC6752 E(B-V) [Fe/H] 0.04
Main sequence fitting distance to 47 Tucanae E(B-V) [Fe/H] 0.04
Main parameters for NGC6397, NGC6752 and 47 Tuc Parameter NGC6397 NGC Tuc [Fe/H] 0.04 (m-M) V (from B-V) (m-M) V (from b-y) (m-M) V 0.06 (average) V(TO) 0.05 (new measure) V(HB) 0.10 (using Rosenberg V) M V (TO) 3.98 0.07 M V (HB) 0.53 0.11 Age (Gyr) 14.1 0.8 (Chieffi & Straniero isochrones) Mean Age = 13.1 1.0 Gyr
Comparison between location in the cmd of stars of NGC6397 and field subdwarfs with parallaxes error / <0.12 and -2.43<[Fe/H]<-1.63 Green points are bona fide single stars; red are known binaries
Comparison between location in the cmd of stars of NGC6752 and field subdwarfs with parallaxes error / <0.12 and -1.72<[Fe/H]<-1.12 Green points are bona fide single stars; red are known binaries
Comparison between location in the cmd of stars of 47 Tucanae and field subdwarfs with parallaxes error / <0.12 and -0.76<[Fe/H]<-0.56 Green points are bona fide single stars; red are known binaries
Systematic effects and total error budget associated with the MS fitting distances to Globular Clusters Effect (m-M) Malmquist bias negligible Lutz-Kelker correction 0.02 Binaries (in the field) 0.02 Binaries (in clusters) 0.03 Reddening scale (0.008 mag) 0.04 Metallicity scale (0.04 dex) 0.03 Total uncertainty (1 ) 0.07 Reddening free T eff calibration
Rotation of TO-stars in globular clusters
A consistent fraction of stars on the horizontal branch of globular clusters rotate at rather high velocities (Peterson 1983; Behr et al. 2000a, 2000b) The origin of the angular momentum of these stars is unclear. Given the large cluster ages, a low rotation velocity is expected for main sequence stars, due to dissipation by the dynamo mechanism (Skumanich law) However no data have been insofar obtained for main sequence stars in globular clusters
Line FWHM is derived by cross correlating with templates This method can be also used to check for contaminating stars
Line FWHM can be calibrated in terms of rotation velocities (or upper limits of) using stars with known rotational velocities
TO-stars and subgiants in globular clusters are very slow rotators. Upper limits to rotational velocities are obtained by subtracting broadening due to microturbulence from the FWHM
If stars rotate, scatter is expected depending on random orientation of the rotational axis Very stringent upper limits to rotation can be obtained by comparing the observed scatter with that expected from random axis orientation The limit is: v sin i 1.7 km/s The limit on rotation is v 2 km/s
- NGC 6397 is a very homogeneous cluster ([Fe/H]=-2.03 0.04) - Abundances for TO-stars and subgiants agree within a few percent, costraining the impact of diffusion on stellar models - The O-Na (and Mg-Al) anticorrelation is present among TO stars in NGC6752. This rules out internal mixing as the cause of the O-Na anticorrelation - Stars at the TO of NGC6397, and O-rich TO-stars in NGC6752 have Li abundances very close to those of stars on the Spite’s plateau - Li is anticorrelated with Na in TO-stars of NGC6752; however some Li is observed also in most Na-rich, O-poor stars - Derivation of distances and ages in progress
SPECTROSCOPY Li and Be as probe of stellar Interior L. Pasquini July 2002 Li and Be are the two elements most largely depleted in the solar photosphere; Li is destroyed by proton capture reaction at 2.5 million K ; Be 1 million K hotter. (cfr. Steigman) Li7 is produced by primordial nucleosynthesis, Be by spallation produced by high energy galactic cosmic rays. Current view is that primordial Li is close to the pop II ‘plateau’, then it has enriched by a factor 10 during the Galactic history, to the levels observed in young pop I stars, where is internally destroyed. Its study in Pop II and Pop I stars tells us about Primordial nucleosynthesis and barion density (PopII) Internal structure of the stars and mixing mechanism (PopI ).
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 Li7 is depleted 100 times in the solar photosphere with respect to meteorites. The original gas has been transported to high temperature, or diluted with Li poor gas, or Li has diffused from surface.. Key Observations: Open Clusters (Pasquini et al A&A 325, 535, Pasquini 2000, IAU 198,Natal); 2001, A&A374,1017, Randich et al. 2000, A&A 356,L25; 2002, A&A 387,222 ) + Homogeneous, Known ages + Chemically Homogeneous (?) sample + Well determined relative parameters + Good (but not excellent!) age and metallicity distribution in the Galaxy - FAINT ! > Large Telescopes, State-of-the-art instruments.. - Be lines are in the UV, at 313 nm UVES !!!!
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 Li on Pre- Main Sequence. IC2602, 2391, 4665 are young, a few million years old. G stars are on M-S, K stars not yet. They also have different metallicities. G stars have Li abundances very close to the solar meteoritic value (LogN(Li)=3.3)) ----> No PMS depletion Colder stars (K stars, below 5000 K ) show a clear signature of depletion, may be metallicity dependent on PMS Note that there is almost no difference with much older (100 Myr) Pleiades.
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 Li on Main Sequence Hyades (700 Myr) IC4651 and NGC3680 (1.6 Gyr) M67 (4 Gyr). Main sequence depletion is present among G stars, most action in the first Gyr(s). No spread is observed at a given T up to ~1.6 Gyrs. Dual behaviour for older stars, (M67), factor 10 difference, as observed in the field.
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 The Li behaviour in open clusters does not quantitatively agree with models, either ‘classical’ (e.g. where only convection is acting) or ‘mixing’ ones (e.g. rotationally induced mixing, Pinsonneault et al. 2000, IAU 198, Natal)
SPECTROSCOPY Be in Pop I stars L. Pasquini July 2002 Since Be is destroyed at higher temperatures, Li-Be diagrams are powerful tests for stellar interior models (see e.g. Delyiannis et al IAU 198, Natal) Be is in the UV, in a CROWDED region ----> HR UV spectrograph + Spectral synthesis
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 Crucial test: In M67 main sequence stars exist with same effective temperature, but Li abundances difering by a factor 10. UVES + dychroic simultaneous observations (Li and Be) up to V=14.3 !!! That is about 2 magnitude fainter than any previous Be observations ! While Li differs > Be is the same The MIXING MUST BE SHALLOW ! Enough to burn Li, but not Be.
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 Rotationally -induced mixing models have precise predictions : Li depletion must be accompanied by some degree of Be depletion. The line shows predictions from models. The constancy of Be abundance regardless of Li (as well other parameters, such as age) is impressive.
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 Out of possible models, only gravitational waves are compatible with the observed behaviour of Be(point-dashed lines). All other models (diffusion, rotational induced mixing) would predict too much Be depletion.
SPECTROSCOPY Li and Be in Pop I stars L. Pasquini July 2002 Gravitational waves alone (point-dashed models for 1.7 and 4 Gyrs), however, are primarily functions of fundamental stellar parameters, so they cannot explain the observations of Li star to star variations in M67 and field stars (including the Sun). Dashed lines: rotational models of 1.5 and 4 Gyrs for starting rotational velocity of 30 and 10 Km/sec respectively.