1. The SCORPIO project: Stellar Radio emission in the SKA era
Francesco Cavallaro
Group: Corrado Trigilio, Grazia Umana, Adriano Ingallinera, Paolo Leto, Carla Buemi, Filomena Bufano, Simone Riggi, Luciano Cerrigone, Claudia Agliozzo, Ray Norris, Thomas Franzen, Joshua Marvil
NGC 6231

2. Stellar
Continuum
Originating from
Radio
Physics In
Ourgalaxy
NGC 6231

3. Two main goals: SCORPIO
A deep survey of a wide region of the Galactic Plane
Two main goals:
Scientific
Very few stars are known as radio emitter
How many stars can be detected with EMU, SKA...?
What is the occurrence (in radio) of different class of stars?
Technical
Test bed for the EMU/SKA surveys: strategy for the GP section.
Source complexity: issues due to complex structure in the GP
Source variability: issues due to the variable sources in the GP
Source finding: issues due to in the diffuse emission in the GP
Source identification: how identify different populations (e.g. Galactic from Extragalactic, different type of stars)?

4. Radio Stars: HR Diagram
SCORPIO
Radio Stars: HR Diagram
Only 420 radio stars detected so far, mainly VLA results
(Gudel, 2002)
Lradio a small fraction of Ltot (10-13 for the Sun)
Radio probes astrophysical phenomena non
detectable by other means:
B and its topology in flares stars, RS CVn
HII region in dust enshrouded sources
Winds-winds interactions….
Important for:
Stellar evolution, interaction with ISM
Physical processes in a wider context.

5. The brightest stellar radio emission associated with:
Radio Stars: The tip of the iceberg Jy
The brightest stellar radio emission associated with:
small TB
Large emitting surface
Thermal radio source
Usually PMS or evolved stars
Bremsstrahlung
Not variable
high TB
Small emitting surface
Non- thermal radio source
Can be MS stars
Synchrotron / Gyrosynchrotron
Variable

6. Stellar radio emission Thermal: Luminous Blue Variable
Thermal radio emission associated with:
-Large mass-loss (large emitting surface): free-free from stellar winds (OB, WR)
Sν≈να α=0.6-2
VLA-A, 5 GHz (6cm)
Current day mass-loss
Myr-1
Montes et al. 2011
VISIR m
Mion2 MSun
IRAS
Buemi et al., 2012
B0-B0.5 I,
Teff ~ K
Umana et al., 2005

7. Stellar radio emission Thermal: Planetary Nebulae
Ingallinera et al., 2016
Gruenwald and Aleman 2007

8. Stellar radio emission Non thermal: Magnetic stars
Early type stars (main sequence B-A)
Magnetic Chemically Peculiar Stars
Flat spectra (few mJy level)
25 % of magnetic stars radio emitters b
The radiation pressure is hight enought to drive an high velocity ionized stellar wind.
In the regions of the magnetosphere where the wind pressure exceeds the magnetic pressure, close to the polar regions, the filed lines are open and the wind flows freely.
Conversely, in the equatorial regions the wind cannot escape, leading to the formation of a torus-like nebula.
Just out of the Alfven radius, the open field lines generate current sheets, where the ionized particle of the wind are accelerated up to relativistic energies. They eventually come back to the stars following the lines of the field, emitting via gyrosynchrotron, and then are reflected out by magnetic mirroring. The study of the physical conditions of this transition region is the aim of our model.
Gyrosynchrotron emission
interaction wind-magnetic dipole
Stable emission (rotation modulated)
Figure from Montmerle, 2001
Surveys:
Drake+ (1987), Willson+ (1987), Linsky + (1992), Leone Trigilio Umana (1994)

9. Stellar radio emission Non-Thermal: CP Stars
Leone et al. 2004

10. Stellar radio emission Status
The actual knowledge of stellar radio emission suffers of:
-limited sensitivity:
No radio star with radio luminosity similar
to the quiescent Sun (L6cm ≈ erg sec-1 Hz-1)
detected yet.
-selection bias:
based on targeted observations aimed at addressing
a specific astrophysical problem
Flares stars (and late-M) Seaquist, 1993; Gudel 2002; Berger et al. 2005
PMS Gudel, 2002
Active binary systems Moris and Mutel, 1988, Umana et al., 1993
OB-WR Seaquist, 1993; Bieging et al., 1989
MCP Leone et al., 1992; Trigilio et al., 1994

11. Stellar radio emission EMU / SKA Forecast
SKA – 1h
With a limiting flux of 30 μJy:
flare stars (quiesc) detected up to 20 pc, RS (quiesc) up to 500 pc
PMS, CP and WR/OB at 1-8 kpc (GC)
Adapted from Umana et al. 2016

12. Stellar radio emission EMU / SKA Forecast
Key question:
How many stars, at sub-mJy level, we can expect to detect in one square degree?
Not obvious answer
The presence of stars belonging to classes thought to be radio emitter is a necessary but not sufficient condition to detect them. Need sufficient B and Nrel (non-therm) or mass-loss rate and UV field (therm). Detection rate: OB/WR 20%, MCP 25%, 30-40% RSCVn
Depends on the radio luminosity and sensitivity of the survey (distance plays a role).
Variability of non-thermal and coherent radio emission.
Can existing large field radio surveys help?
NVSS, too shallow and low angular resolution for stellar work
FIRST, ATLAS,…designed for extragalactic High Galactic Latitude

13. A deep radio survey in the GP with the ATCA
SCORPIO
The project
A deep radio survey in the GP with the ATCA
Same observing strategy as ATLAS
Frequency 2GHz (as EMU); High Sensitivity (σ≈30 mJy beam-1)
In a sky patch well suited for stellar work, i.e. low Galactic latitude

14. In the tail of SCORPIO SCORPIO The selected field l=344.25 b=0.50
2° x 2°
2 deg
Close to the GP, extending high b
A “sufficient” number potential radio stars
Few radio sources already detected in it: to be used as check
Multi-λ observations available for comparative studies. GP

15. SCORPIO
The selected field
2 deg GP

16. SCORPIO The selected field SCO OB1 association
NGC 6231, a young open stellar cluster (3-5 Myr) at D=1.6 kpc, 964 stars
(OB, PMS, X-ray...)
A total of 8 stellar clusters, associations
Many inside “bubbles” discovered with 2MASS, Glimpse
2 deg GP

17. Other Surveys in SCORPIO
Spitzer
GLIMPSE , 4.5, μm
MIPSGAL 24, 70 μm
(Benjamin +, 2003, Carey +, 2009)
HERSCHEL
Hi-GAL 70, 160, 250, 350, 500 μm (Molinari +, 2010)
MOLONGLO 834 MHz (MGPS)
Sydney University Molonglo Sky Survey
(Mauch +, 2003)
ATCA
CORNISH-S 6+9 GHz
(PI: Hoare)
MeerKAT GP survey 14GHz
(PI: Thompson)
2 deg GP

18. SCORPIO
The Sub-Bands

19. Pilot experiment: the map
SCORPIO
Pilot experiment: the map
The field has been mapped in Stokes I and V to compare noise
Noise I ~ 10 x Noise V in GP
Presence of diffuse emission
Need to improve imaging in GP
Stokes I
Stokes V
Best S/N
Umana et al., 2015

20. SCORPIO
The whole map GP
Best S/N

21. SCORPIO Map analysis in GP
For the two maps with 6a and 6B configs, LAS is inadequate for the source extension
bubble S17: size 1’, 10’
Bmin= 3 kl LAS=3’
Bmax= 40 kl res=5”
artfacts:
deep negatives
loss of flux in extended sources
high rms (σ≈ mJy/beam)
prevents to detect point sources

22. SCORPIO Map analysis in GP Adding short baseline obs: EW367 config
Bmin= 400 l LAS=18’
Bmax= 40 kl res=5”
Map obtained in Miriad
Adequate to bright extended sources

23. SCORPIO
The final map GP

24. Preliminary combination tests with SGPS data:
SCORPIO
Adding Single Dish data
Preliminary combination tests with SGPS data:
classical feathering (casafeather)
creating a visibility dataset from SGPS images, concatenating with ATCA visibilities, CLEANing
SGPS/Parkes
DATA
CREATING FILTERS and VISIBILITIES WEIGHTS
DFT
CONCATENATING
CLEAN
ATCA DATA 10

25. Adding Single Dish data
SCORPIO
Adding Single Dish data 10

26. Adding Single Dish data
SCORPIO
Adding Single Dish data 10

27. SCORPIO
Parkes data 10

28. Spectral indices algorithm
SCORPIO
Spectral indices algorithm
Source coordinates reading
Boxes creation
Boxes Control
IMFIT
IMSTAT
Fit parameters variable
Rms median of the 4 boxes
Fit parameters return
Cavallaro et al., submitted

29. Spectral indices algorithm
SCORPIO
Spectral indices algorithm
Reading
Fluxes and errors
Elimination of fluxes Si≤0
Positional error point elimination
Area Error point elimination
Elimination
|Si - S| ≤nS
Fitting
Parameter gaussian fit reading
Fit peak position reading
Positional error point writing
Linear fit parameters return
Cavallaro et al., submitted

30. Spectral indices algorithm
SCORPIO
Spectral indices algorithm
Cavallaro et al., submitted

31. Spectral Indices Analysis
SCORPIO
Spectral Indices Analysis
Cavallaro et al., submitted

32. Spectral Indices Analysis
SCORPIO
Spectral Indices Analysis
Cavallaro et al., submitted

33. Spectral Indices Analysis
SCORPIO
Spectral Indices Analysis
Cavallaro et al., submitted

34. Spectral Indices Analysis
SCORPIO
Spectral Indices Analysis
Cavallaro et al., submitted

35. Spectral Indices Analysis
SCORPIO
Spectral Indices Analysis
Cavallaro et al., submitted

36. SCORPIO
SCORPIO - ATLAS
Cavallaro et al., submitted

37. SCORPIO
WORK IN PROGRESS: Polarization

38. WORK IN PROGRESS: CAESAR
SCORPIO
WORK IN PROGRESS: CAESAR
Compact and Extended Sources Automated Recognition
Riggi et al., 2016

39. Scorpio The whole map Radio Galaxy SFR SNR Stars in open cluster
Star WR 78
Evolved stars?
SFR?
Star ζ1Sco
SFR ?
SFR

40. Conclusions What did we learn from this project? Scientific results:
We detected 20% more compact sources brighter than 1mJy, almost all of them in the flat or inverted spectral indices region in respect of the high Galactic latitude surveys. These sources can be HII regions, evolved stars or MS stars.
We detected lots of extended sources: SNR, HII regions and generic bubbles (SFR or PNe).
Technical results:
We developed an algorithm to authomatically extract the spectral indices of the compact sources
We developed an algorithm to authomatically find extended sources (CAESAR)
We found lots of issues on the GP (diffuse emission, artefacts…) that prevent a good imaging of the field. We’ll find the same issues in the future surveys.
We worked on an algorithm to better combine single dish and interferometric observations.