Stellar radio emission in the SKA era: the SCORPIO project
Grazia Umana INAF-OAC
C. Trigilio, R. Norris, T. Franzen, A. Ingallinera, C. Agliozzo P. Leto, C. Buemi, E. Budding, B. Slee, G. Ramsay, G. Doyle, M. Thompson, J.C. Guirado, S. Keller, J.D. Bunton, J. Lazio, F. Leone, G. Hallinan, M. Johnston-Hollit, G. Hobbs, M. Mao
Stellar radio emission
HR diagram for the 420 radio detected stars (Gudel, 2002)
-Lradio a small (10-12 Sun) fraction of Ltot
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 -Physical processes in a wider context.
Stellar radio emission
The brightest stellar radio emission associated with:
-Large mass-loss (large emitting surface): free-free from stellar winds (OB, WR) Sν≈να α=0.6-2
-Solar-type, non-thermal phenomena (high TB): gyrosynchrotron, related to a strong and (often) variable stellar B
• Gyro-synchrotron (Active stars and stellar systems): quiescent periods -slowly varying flux density, up to several mJy active periods -series of strong outburst, up to 1Jy Variable
Active binary systems
Active periods can last several months Noto 6cm monitoring- 23 days/ up to 12 hrs coverage
Both quiescent and active periods are Related to solar-type magnetic activity (observed also in other spectral ranges)
Radio flares in large magnetic structures (loops); in binaries could be intersystem: Algol (Mutel et al., 2009)
Stellar radio emission
Astrophysical environments common ingredient strong B and energetic particles
Active stars and stellar systems (Osten et al., 2004; Slee et al., 2008..)
Ultra Cool Dwarf (Hallinan et al., 2008)
CPs stars (Trigilio et al., 2000; Trigilio et al., 2008, 2011)
Coherents events (usually observed in addition to gyrosynchrotron) • Modelled as electron cyclotron maser emission (ECME)
Polarization up to 100% Frequency structure Narrow bandwidth Short duration (time)
Usually observed at low-freq < 2.5 GHz.
General Characteristics
See Trigilio talk…..
Slee et al., 2008
HR 1099
1.384 GHz
2.368 GHz
ATCA
Δt ∼2-3 hrs
Active binary systems
-Both incoherent (gyro-syncrotron) and coherent emission
Hallinan et al., 2006, Berger et al., 2009 McLean et al., 2011
TVLM 513-46546 M9
LCP
RCP
VLA, X,C simultaneous -2 epochs , 10 hrs each -folded with P= 1.96 hrs
Stable magnetic structure?
Late M
Stellar radio emission
The actual knowledge of stellar radio emission suffers of:
-limited sensitivity:
No radio star with radio luminosity similar to the quiescent Sun (L6cm ≈ 1011 erg/sec Hz) detected yet. -selection bias:
based on targeted observations aimed at addressing a specific astrophysical problem
However, starting from some information on radio luminosity………
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 CP Leone et al., 1992; Trigilio et al., 1994
We can build … a stellar radio emission forecast
Schematic radio continuum spectrum of several classes of radio emitting stars
Assumed distances are: 10pc flare stars, 100pc RS and PMS, 500pc CP, 1kpc OB and SG
Stellar radio emission forecast
With a limiting flux of 30 μJy:
flare stars (q) detected up to 20pc, RS (q) up to 500pc PMS, CP and WR/OB at more than 1kpc
Stellar radio emission forecast
Not obvious answer
1) 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 20%, CP 25%, 30-40% RS
2) Distance plays a role
3) Non-thermal radio emission is variable
Key question:
How many stars, at sub-mJy level, we can expect to detect in one square degree of sky?
Can large field radio survey help? NVSS, too shallow and low angular resolution for stellar work FIRST, ATLAS,…designed for extragalactic High Galactic Latitude
The SCORPIO Project
A deep radio survey with the ATCA
-same observing strategy as ATLAS
-in a sky patch well suited for stellar work, i.e. low Galactic latitude
Expected outcomes- Science
- Enlarge the stellar radio emitting population, with no selection bias
- Better comprehension of physics and plasma processes
- Establish how common are coherent events among stellar sources.
The SCORPIO Project
Expected outcomes- Planning the EMU project
Results from SCORPIO will guide EMU in the following areas:
- Dynamic range from sources complexity: issues related to complex, extended structure in the GP
- Dynamic range from source variability: issues related to the presence of variability in most of non-therm sources
- Source extractions: what is the most appropriate method for sources embedded in the diffuse emission in the GP
The selected field: requirements
Close to the galactic Plane (GP) but not only in the GP: extended emission could be a severe issue
A “sufficient” number of stars , good spread in classes of radio emitting object
Few radio sources already detected in it: to be used as check
Multi-λ observations available for comparative studies.
The selected field
In the tail of SCORPIO
The selected field
2 x 2 deg2
L=343.5 B=1.0
NGC 6231 SCORPIO OB1
IC 4628
The selected field
2 x 2 deg2
L=343.5 B=1.0
NGC 6231 SCORPIO OB1
IC 4628
The selected field
Quering SIMBAD…….
Stars: WR, Delta Scu Algols, Var, Double Em Line
The selected field
Part of sky patch has been surveyed by:
• Spitzer (Benjamin et al., 2003, Carey et al., 2009) • HERSCHEL (Hi-GAL, Molinari et al., 2010)
And will be observed in: • CORNISH-S (PI: Hoare) • MeerKAT GP survey (PI: Thompson)
The pilot experiment 0.5 x 2 deg2, l=344, b=0.66
Observed in mosaic mode with ATCA 38 pointings, 8.8 arcmin spacing hexagonal grid
Duty cycle=1min/pointing +cal total integration time/pointing 1hr Total observing time= 48hrs (4 days)
C2515 6A Δν= 1.1-3.1 GHz CABB: 2048 chs, 1 MHz each
HPBW of the ATCA antennas centered on the pointing pos.
The pilot experiment:
Searching for the best strategy…
RFI a nightmare! -help from mirflag but should used with some preacutions -Need to take care for SEDs of sources within the bandpass
- Data flagging and calibration performed in MIRIAD
- Map making: in its VERY VERY early phase….
- MOSAIC: individual approach (MIRIAD)? or direct (CASA)?
The pilot experiment
-About 50 islands found by imsad (>5 rms) -no matchs with NED - 5 matchs with SIMBAD (search radius 10”)
1 pointing, 300 MHz (2 GHz) mfs rms ≅90 μJy
The pilot experiment
Evident side-lobes
Need checks for calibrations errors And/or RFI effects left
No selfcal
1 pointing, 300 MHz (2 GHz) mfs rms ≅90 μJy
FOV≈20’ x 15’
The pilot experiment
Sub-mosaic (7 pointing) CASA, mfs Bandpass in 3, 300 MHz sub-bands 1.5 GHz, rms=140μJy, B=11.5” x 6.6” 2.1 GHz, rms=140μJy, B=8.9” x 5.1” 2.9 GHz, rms=100μJy, B=6.7” x 3.7”
Use of the large bandpass to get spectral information FOV ≈ 1° x 0.5°
