An evolutionary sequence for high-mass stars formation

Transcription

1 Introduction Results & Conclusions Summary An evolutionary sequence for high-mass stars formation Andrea Giannetti Dipartimento di Astronomia, Università di Bologna; Istituto di Radioastronomia In collaboration with INAF-IRA, Bologna (Brand), INAF-OA Arcetri, Firenze (Cesaroni, Sanchez-Monge, Fontani, Beltran) and INAF-IAPS, Roma (Molinari) 1 October 2013

2 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations Formation of High-Mass Stars Starless cores HC/UCHii regions Hot cores Pre/Proto-stellar cores Hii regions

3 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations Formation of High-Mass Stars Open Issues: Mechanism through which the massive stars accrete their mass Physical process responsible for the observed IMF Initial conditions for massive star clusters formation and how they arise Duration of the star cluster formation process Influence of the stellar feedback

4 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations Background Past 20 yr: Extensive investigation of luminous IRAS sources over the whole sky Selected to have FIR colours typical of YSOs Observed at several λ and resolutions Several mm clumps around an IRAS source

5 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations

6 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations What do we want to know? Accurate temperature determination Why? Distance for each of the mm clumps Luminosity for each of the mm clumps Accurate masses and densities Information on the environmental conditions in the first stages of massive star/cluster formation Stability analysis Evolutionary stage of the clump Do these properties depend on the evolutionary stage?

7 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations What do we want to know? Accurate temperature determination Why? Distance for each of the mm clumps Luminosity for each of the mm clumps Accurate masses and densities Information on the environmental conditions in the first stages of massive star/cluster formation Stability analysis Evolutionary stage of the clump Do these properties depend on the evolutionary stage?

8 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations What do we want to know? Accurate temperature determination Why? Distance for each of the mm clumps Luminosity for each of the mm clumps Accurate masses and densities Information on the environmental conditions in the first stages of massive star/cluster formation Stability analysis Evolutionary stage of the clump Do these properties depend on the evolutionary stage?

9 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations How can we get this information? ATCA interferometer

10 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations How can we get this information? NH 3 (23 GHz): Traces dense, cold gas Excellent thermometer 5 hyperfine components Does not deplete up to high H 2 volume densities H 2 O masers (22 GHz): Excited by the interaction of the protostellar outflow and the surrounding environment Reveal ongoing star formation

11 Introduction Results & Conclusions Summary Introduction Past Work Methods and Observations Spectral Energy Distribution: Gathered Spitzer and MSX data in addition to the SEST and Hi-GAL Possible to construct a SED Smoothing of the images to the same resolution (25 ) Derive the luminosity Derive T d, M, β from a greybody fit (down to 70 µm)

12 Results Integrated Emission Ammonia emission traces well the 1.2mm-continuum emission Greyscale: 1.2 mm-continuum Contours: Ammonia

13 Results Good agreement T K and T d in the range K Column, volume and surface densities: N H cm 2, n H cm 3, Σ 0.2 g cm 2

14 Results Kauffmann & Pillai derived an empirical threshold for massive star formation. Virtually all clumps are found above the threshold Good sample to study the initial conditions and evolution of the HMSF process

15 Results α M vir/m 1.2mm Clumps appear dominated by gravity, but: Magnetic field Rotational support not taken into account

16 Problem: How can we define an evolutionary sequence for massive clumps?

17 By identifying sources with/without ongoing star formation 24 µm emission H 2 O masers Radio continuum emission (1.3cm) Green Fuzzies Greyscale: 24 µm Contours: 1.2 mm

18 Red: 8 µm Green: 4.5 µm Blue: 3.6 µm By identifying sources with/without ongoing star formation 24 µm emission H 2 O masers Radio continuum emission (1.3cm) Green Fuzzies Extended excess of 4.5 µm emission Molecular lines (CO, H 2) Trace shocked gas produced by the interaction of the central object and the surrounding material

19 Results : QS : SFS : MSX : Radio Cont. time time The evolutionary phase is visible in the M-L plot Extension of the relation for low-mass stars ZAMS SFS is a broad class, containing a range of evolutionary phases

20 Results : QS : SFS : MSX : Radio Cont. time time The evolutionary phase is visible in the M-L plot Extension of the relation for low-mass stars ZAMS SFS is a broad class, containing a range of evolutionary phases

21 Results : QS : SFS : MSX : Radio Cont. time time The evolutionary phase is visible in the M-L plot Extension of the relation for low-mass stars ZAMS SFS is a broad class, containing a range of evolutionary phases

22 SED Flux(Jy) Change in the SED shape approaching the ZAMS: 3 µm λ 3 mm Cold, quiescent clumps have an SED consistent with a greybody Luminous and active clumps have considerable emission also in the mid-ir

23 SED Change in the SED shape approaching the ZAMS: Cold, quiescent clumps have an SED consistent with a greybody Luminous and active clumps have considerable emission also in the mid-ir

24 SED Change in the SED shape approaching the ZAMS: Cold, quiescent clumps have an SED consistent with a greybody Luminous and active clumps have considerable emission also in the mid-ir

25 Conclusions QS SFS Star-forming sub-sample: Higher luminosities On average shows higher T K, T d and n H2 L increases with T

26 Conclusions Type 1, QS Type 1, SFS Type 2 Type 2 Sources: Higher temperature ( 22 K) n H cm 3 N H cm 2 Σ 0.4 g cm 2

27 Conclusions Type 2 Sources: Smaller FWHM size More centrally concentrated Steeper power law for the density profiles

28 Introduction Results & Conclusions Summary TK Td 13 K N(H2) cm 2 n(h2) cm 3 L/M 1 L M 1 Σ 0.1 g cm 2 QS SFS-1 Massive Outflow TK Td 17 K N(H2) cm 2 n(h2) cm 3 L/M 2 L M 1 Σ 0.2 g cm 2 Clump Cores High-mass Proto-star Low-mass (Proto-)star HC/UCHii Region TK Td 23 K Hii Region Type 3 High-mass ZAMS Star SFS-2 N(H2) cm 2 n(h2) cm 3 L/M 24 L M 1 Σ 0.4 g cm 2

29 Introduction Results & Conclusions Summary Thank you!