Image of the Week

Gaia captures a rare FU ORI outburst

 

Figure 1: Lightcurve measured by Gaia (G-band with effective wavelength of 0.673 micron) in blue filled symbols and NEOWISE (3.4 and 4.6 microns) in black and red filled symbols. The horizontal axis denotes time in days [MJD]. Added to the recently obtained photometric data is the previously obtained information on this source by the IPHAS and PanSTARRS surveys in the optical, corrected from the r-band to the G-band, as well as the information obtained from Spitzer in the infrared, plotted as the native 3.6 and 4.5 micron measurements, without correction. This additional information is indicated with open symbols. The downward pointing arrows indicate the epochs of position coverage by the WISE sky survey, in which the source was not detected. Credit: Hillenbrand et al. 2018.

FU Orionis stars are young, near-infant variable stars named after their prototype in the constellation of Orion, displaying an extreme change in magnitude and spectral type. These type of stars are important for star formation theories, and their outbursts are thought to be the main way in which stars acquire their mass, after the initial gravitational collapse and the formation of the "protostar". To better understand star formation and the differences between observations and theories, FU Orionis stars and their outbursts are essential.

While these objects are important for this field of study, it still remains a mystery why we do not see very many of them. To date, only about 25 FU Orionis stars are known, while only a dozen were actually observed to undergo an outburst. These outbursts are therefore rare events, much more rare than for example a supernova or even tidal disruption events. Finding a FU Orionis object is thus very special, and finding one that is outbursting is an exceptional opportunity.

While Gaia scans the sky (see the scanning illustrated in the video below), it repeatedly observes sources. Over its nominal lifetime of 5 years, Gaia is expected to see each source on average 70 times. Hence, when the brightness of a source rises or falls, it will be visible in the Gaia data. To allow for a timely follow-up of transient events, a significant change in source brightness in the Gaia data can trigger an alert and the information on the source is then shared through the Gaia Photometric Science Alerts webpage allowing scientists to observe the event with other observatories.

The paper by Hillenbrand et al. 2018 accepted for publication by ApJ (scheduled to appear in the 20 December issue) describes the discovery of such a FU Orionis object that is undergoing an outburst. This discovery was based on Gaia data which was made public through the Gaia Photometric Science Alerts.

 

Gaia scanning the sky. Video credit: ESA/Gaia/DPAC. Video acknowledgement: B. Holl (University of Geneva, Switzerland), A. Moitinho & M. Barros (CENTRA – University of Lisbon), on behalf of DPAC.

 

These alerts are related to the area Gaia is looking at (to predict which sources Gaia will observe, one can use the Gaia Observation Forecast Tool). An overview of the alerts triggered by the Photometric Science Alerts pipeline (residing at one of the DPAC institutes in the UK: the Institute of Astronomy of the University of Cambridge) is given in the below video.

 

Gaia alerts over time as published by the Gaia Photometric Science Alerts team. Video credit: S. Koposov. When looking closely, one can recognise the scanning law in the pattern of triggered alerts. Also, a gap is visible in the second half of 2015, caused by a verification phase of the alerts system taking place in this period.

 

On June 23 2017, an alert was issued for Gaia17bpi since a difference of about 2 magnitudes was observed with respect to earlier observations of the source by Gaia. The object was flagged as an outburst of a young stellar object. The source continued to brighten since the alert and is currently at a G magnitude of about 17.

Following the Gaia alert, the source was monitored using the Liverpool Telescope. Also the University of Kent's Beacon Observatory performed some additional optical imaging. Apart from following up, Hillenbrand et al. investigated whether the source was detected by other observatories in the past years. It turns out that there were some NEOWISE observations available. The combination of some of the data for Gaia17bpi can be found in Figure 1, which shows the lightcurve of the FU Ori outburst.

 

“Gaia is making a continuous movie of the sky, perfect for catching explosive events in the act. We are so lucky to have seen this rarest of eruptions at both optical and infrared wavelengths which enables us to uncover the physics at work in the youngest stars", says Simon Hodgkin, member of the Gaia Photometric Science Alerts team.

 

The observations by Gaia and other observatories are presented in the paper by Hillenbrand et al. These observations show direct evidence for the initial heating out in the disk (infrared lightcurve from NEOWISE+Spitzer), the subsequent heating of the innermost regions close to the star (optical lightcurve from Gaia), the temperature structure of the disk (spectroscopy from Keck and Palomar), the strong outflow, and the youth of the source (distinguishing it from other types of outburst objects such as cataclysmic variables).

 

Figure 2: Artist's rendition of a FU Orionis outburst in action. This illustration shows a young star undergoing a type of a growth spurt. Top panel: Material from the dusty and gas-rich disk (orange) plus hot gas (blue) mildly flows onto the star, creating a hot spot (bright spot). Middle panel: The outburst begins - the inner disk is heated, more material flows to the star, and the disk creeps inward. Lower panel: The outburst is in full throttle, with the inner disk merging into the star and gas flowing outward (green). Image credit: Caltech/T. Pyle (IPAC)

 

Interested in further reading?

 

 

The location of Gaia 17bpi, which lies in the Sagitta constellation, is indicated in this image taken by NASA’s Spitzer Space Telescope. Image credit: NASA/JPL-Caltech/M. Kuhn (Caltech)

 

Credits: ESA/Gaia/DPAC, S. Hodgkin, L. Hillenbrand, S. Koposov, Gaia Photometric Science Alerts Team, Caltech/T. Pyle (IPAC)

[Published: 18/11/2018]

 

Image of the Week Archive

2019
03/05: Atmospheric dynamics of AGB stars revealed by Gaia
25/04: Geographic contributions to DPAC
22/04: omega Centauri's lost stars
18/04: 53rd ESLAB symposium "the Gaia universe"
18/02: A river of stars
2018
21/12: Sonification of Gaia data
18/12: Gaia captures a rare FU Ori outburst
12/12: Changes in the DPAC Executive
26/11:New Very Low Mass dwarfs in Gaia data
19/11: Hypervelocity White Dwarfs in Gaia data
15/11: Hunting evolved carbon stars with Gaia RP spectra
13/11: Gaia catches the movement of the tiny galaxies surrounding the Milky Way
06/11: Secrets of the "wild duck" cluster revealed
12/10: 25 years since the initial GAIA proposal
09/10: 3rd Gaia DPAC Consortium Meeting
30/09: A new panoramic sky map of the Milky Way's Stellar Streams
25/09: Plausible home stars for interstellar object 'Oumuamua
11/09: Impressions from the IAU General Assembly
30/06: Asteroids in Gaia Data
14/06: Mapping and visualising Gaia DR2

25/04: In-depth stories on Gaia DR2

14/04: Gaia tops one trillion observations
16/03: Gaia DR2 Passbands
27/02: Triton observation campaign
11/02: Gaia Women In Science
29/01: Following-up on Gaia
2017
19/12: 4th launch anniversary
24/11: Gaia-GOSA service
27/10: German Gaia stamp in the making
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
04/10: 1:1 Gaia model arrives at ESAC
31/08: Close stellar encounters from the first Gaia data release
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
2016
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
2015
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
2014
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
2013
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
2012
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
2011
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
2010
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
27/08: Quest for the Sun's siblings
 
Please note: Entries from the period 2003-2010 are available in this PDF document.