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Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Francesco Damiani INAF-Osservatorio Astronomico di Palermo, ITALY Stellar.

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Presentation on theme: "Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Francesco Damiani INAF-Osservatorio Astronomico di Palermo, ITALY Stellar."— Presentation transcript:

1 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Francesco Damiani INAF-Osservatorio Astronomico di Palermo, ITALY Stellar classification using spectral indices Outline A set of spectral indices was defined from the spectral range Å (FLAMES/Giraffe HR15n), enabling derivation of stellar fundamental parameters (T eff, log g, [Fe/H]) for T eff ≤ 8000 K (Damiani et al., A&A, in press, astro-ph ). Now, the technique is being refined to deal with: Fast-rotating late-type stars (>90 km/s for T eff, >30 km/s for log g) SB2 stars, and veiled PMS stars OB stars (and A-F supergiants) Chemically peculiar stars (e.g. Carbon stars, Barium stars, Ap stars)

2 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Some representative HR15n spectra from  2 Vel dataset. Colored bands indicate non-molecular features sampled by our indices. MKGFMKGF

3 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Part 1: Fast-rotating late-type stars The problem: narrow-band indices are sensitive to v sin i as soon as spectral lines become wider than wavelength ranges used. Solution: the effect of rotation broadening was studied for each index, a correction was modeled analytically, and applied to recover “true” index values (assuming v sin i is accurately known). Example: index-index diagrams for artificially broadened, low-v sin i template spectra (black circles) from  2 Vel, up to v sin i = 200 km/s. Blue crosses: Blue crosses: cluster members. H  flux from line core (e.g. strong chromosphere) may leak into line wings (mimicking a CTTS) for large enough v sin i: → this effect can be corrected! WTTS CTTS

4 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Two diagrams used to compute PMS veiling. Fast rotation (>70 km/s) has however a similar effect to veiling: this must be corrected for before computing veiling. Veiled stars

5 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Metallicity estimates (index  ) not badly affected by v sin i. Gravity estimates (index  ) are crucially affected (esp. above ~ 110 km/s). Low metallicity Low gravity

6 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Some good news: the M dwarf/giant discrimination provided by indices  6-  7 is unaffected by fast rotation! Giants Dwarfs

7 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Example of procedure: measured index  (and inferred T eff ) vs. v sin i, and its analytical modeling (black dots). Green triangles: actual data for  2 Vel fast-rotating cluster stars.

8 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Results of rotation correction for  2 Vel dataset: A few (weak) CTTS become WTTS. The cluster sequence becomes narrower! CTTS WTTS

9 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 More results for  2 Vel: Veiling (estimated from both diagrams) becomes lower for several CTTS.

10 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 More results for  2 Vel: Less evidence for differential reddening in (V-I,  ). Less apparent age spread in (T eff, log g).

11 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 A check of results: Black: actual spectra of fast rotating  2 Vel stars. Red: rotation-broadened templates (  2 Vel WTTS). T eff were derived only from spectral indices + rotation correction. Matching templates selected from T eff only, not from spectrum best-fit! T eff change as a result of rotation correction

12 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Part 2: SB2 binaries The problem: similarly to fast-rotating stars, in SB2 systems part of the lines sampled fall outside the extraction regions. Solution: the effect of line doubling for equal-mass SB2 systems was studied for each index, and limits of applicability of the method were determined. No inversion procedure was established, as in general the mass ratio q is unknown. Procedure: we computed synthetic SB2 spectra (up to  (RV) = 200 km/s) from real single-star spectra from  2 Vel, and built index-index diagrams.

13 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Binarity has a similar effect to fast rotation!

14 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Its adverse effect is almost irrelevant for T eff determination for  (RV) ≤ km/s (i.e., 50-70% of SB2 in  2 Vel)...

15 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May while gravity determinations are compromised at  (RV) ≥ 25 km/s!

16 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Part 3: veiling in PMS stars The problem: disentangling the (qualitatively similar) effects of veiling and fast rotation on spectral indices. Both phenomena are frequent in CTTS. Solution: after applying the rotation correction to indices, veiling r can be determined as in Damiani et al. (2014). The Chamaeleon I cluster permits a good test of the procedure.

17 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 CTTS veiling r is determined from each of these diagrams separately:

18 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 The adopted veiling r is an average of the two values r 1 and r 2, (note their non-independent errors). Their correlation is a consistency check: r2r2 r1r1

19 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May then other indices are un-veiled accordingly.

20 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Example of results for Cha I: Lithium EW vs.  (~ T eff ), all veiling-corrected. Some spectra over-corrected? (also note the correlated EW – T eff errors).

21 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Check of veiling-corrected Cha I CTTS spectra (black) and same-T eff zero-veiling template spectra of  2 Vel members (red). T eff was derived only from indices. Again, these are not spectral fits!

22 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Part 4: OBA stars The problem: our spectral indices were originally developed for stars later than ~ A5. Occasionally, earlier-type stars are also observed with HR15n: we should be able to classify them as well. Solution: dominant spectral features of OBA stars in the range Å were studied using UVES-POP library spectra, and a new set of indices was defined to recover their spectral type and (sometimes) luminosity class. Additionally, the new indices are able to classify A-F supergiants, which were not satisfactorily dealt with using the original indices. Specific issues for early-type stars in HR15n wavelength range: Few spectral lines Fast rotation Frequently, strong DIBs Emission lines Luckily, the HR15n range includes “hot” lines from He I, He II, C II, Ca II.

23 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Why our temperature index  fails for OB stars? On the MS, since H  changes behaviour when crossing type A0! For supergiants, this change occurs at colder T eff. UVES-POP spectral library

24 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 UVES-POP templates in HR15n range, and spectral features used for new indices.

25 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014

26 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014

27 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 → a “hot” temperature index  h : (not valid later than ~A5, where we have the “old”  ) Emission-line OBA stars (and some peculiar stars) remain problematic even for  h... However, to discriminate F-G supergiants from higher-gravity stars we still need...

28 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 … a “hot” gravity index  h : using (mostly) H  wings and Ca II lines, selects well A-F supergiants. Earlier than ~A0, H  emission may render  h unusable as a gravity indicator. Class V stars form a regular sequence near the bottom. Class III OBA stars not distinguishable from Class V...

29 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 A  h,  h ) diagram for selection of stars requiring use of the “hot” indices: (all except in the grey zone)

30 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 With this selection, the diagram (  h, spectral type) for OB stars and AF supergiants becomes: Best-fit residual rms deviation ~2.5 subclasses (excluding emission-line stars and extreme outliers, of luminosity class 0/I !)

31 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Part 5: chemically peculiar stars The problem: our gravity index  for late-type stars relies largely on the 6497 Ba II line. Therefore, gravity estimates may be inaccurate in stars with a Ba overabundance (or s-element overabundance). Solution: we defined: a new s-element-free gravity index  2. a s-element index , to select stars rich of s-elements. Typically, the s-element-rich late-type stars are slowly-rotating giants: indices may thus be safely defined using very narrow and selective bands. For the same reason, the new gravity index does not substitute our older index  for young, faster-rotating stars.

32 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Examples of Ba-rich (bottom) and Ba-normal (top) giants (from  2 Vel dataset): Green regions: Ba I/II, Y I/II, Sr I, Zr I lines in HR15n, used to define index . Red regions: gravity sensitive lines, used to define index  2.

33 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Indices  2 and  vs. T eff (for  2 Vel dataset): s-element-excess (field) stars are found above a limiting line in ( , T eff ). Black: known chemically peculiar stars from Tomasella et al. (2010).

34 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May but what about NGC6705? A very narrow sequence in  2 between K; instead, many stars scattered above the “regular” sequence in , where known Ap & SrCrEu stars lie... (yet WEBDA lists only one Ap star in NGC6705): What are these s-rich stars?

35 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May are they field stars, like the Ba stars in  2 Vel? Probably not, their RVs being too much clustered!...are they just noisy data? No: their S/N is on average larger than typical cluster stars!...are they evolved cluster stars, e.g. AGB stars? Unlikely, given their CMD position. One possibility: second-generation cluster stars, formed from s-element enriched material? (Cantat-Gaudin et al., submitted, find no enrichment...)

36 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Conclusions We obtain good T eff and [Fe/H] for fast rotators (up to 200 km/s) and log g up to 100 km/s. SB2 T eff and [Fe/H] obtainable for  (RV) up to km/s; log g up to 25 km/s. Good parameters for veiled CTTS, except a few over-corrected cases. OB star T eff obtained using new  h index; supergiant/dwarf distinction using new index  h. S-element excess stars identifiable thanks to new  index: some s- element-enrighed stars in NGC6705?

37 Francesco Damiani Young Clusters in the Gaia-ESO Survey, Palermo, 20 May 2014 Conclusions - 2 Problem: by now, you are maybe so (rightly) scared of all this complexity that you will never use this method... Solution: a forthcoming Web tool will help you: the StarClass stellar classification service (URL still TBD). You submit FITS spectra, and it provides stellar parameters: a first version (not including recent improvements) is ready right now!


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