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Star formation in the Local Group

19 Febbraio 2019 @ 11:45 - 12:45

Using Hubble Space Telescope (HST) observations, we have identified and
characterised almost 50,000 pre-main sequence (PMS) stars in several
star-forming regions in the Milky Way and Magellanic Clouds. These objects
are still undergoing active mass accretion, as revealed by excess emission
in the Halpha band. Detailed knowledge of the extinction law in these
fields, which we derive directly from the observations, allows us to
accurately obtain stellar physical parameters (temperature, luminosity,
age, mass, and mass accretion rate). This is presently the largest and
most homogeneous sample of PMS objects, on which we are conducting the
first comprehensive and systematic study of the PMS phase, spanning a wide
range of masses (0.5-4 Msun), metallicities (0.1-1 Zsun) and ages (0.5-30
Myr).

I will discuss how star formation has proceeded in these regions over
multiple recent bursts and how the accretion process depends on the
physical properties of the individual stars and of the environment. We
have discovered an important dependence of the mass accretion rate on
metallicity: mass accretion rates for stars of the same mass and age are
systematically higher in the Magellanic Clouds than in the Milky Way and
are expected to have been equally high at redshift z~2, when star
formation was at its peak in the Universe. I will also show a surprising
anti-correlation between the variability and intensity of the Halpha
excess: this suggests a discrete and clumpy nature for the accretion
process and reveals that the characteristic mass of the infalling parcels
of gas is comparable to that of the moons of giant planets in the solar
system.

To close, I will illustrate how we plan to thoroughly verify these results
spectroscopically and to extend them to lower mass objects and to more
extinguished environments through already planned guaranteed-time
observations with the James Webb Space Telescope. Our measurements will
provide, for the first time, quantitative information on the nature,
excitation, and kinematics of the infalling gas in these dense environments.

Dettagli

Data:
19 Febbraio 2019
Ora:
11:45 - 12:45
Categoria Evento:

Oratore

Guido De Marchi (ESA)

Luogo

Aula Gratton

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