Image of the Week

 

Observation of a long-predicted new type of binary star

 

Selection of the sample in the colour-magnitude diagram. This sequence of images shows the various steps undertaken to clean the sample before pursuing a follow-up of the most interesting sources. As a comparison, the 100 pc sample (the Gaia Catalogue of Nearby Stars) is given which is shown in black. From top left to right bottom the selection is done as follows: 1. The inital query is given. 2. Quality cuts are applied. 3. Only the variable stars are kept using the Gaia variability classifications. 4. The sample is cross-matched with ZTF  and a quality cut is done on the ZTF light curves. 5. Selection of the ones that show a large-amplitude ellipsoidal variability and an orbital period below 6 hours. 6. A correction for the extinction is performed. Credit: Kareem El-Badry, et al. 2021 MNRAS

 

By combining data from different surveys and organising follow-up observations of selected candidates, a team of researchers has observed a new type of binary star that was long predicted to exist. The discovery finally confirms how such a rare type of star in the universe forms and evolves. The results have been described in Monthly Notices of the Royal Astronomical Society in the paper "Birth of the ELMs: a ZTF survey for evolved cataclysmic variables turning into extremely low-mass white dwarfs" by Kareem El-Badry et al.

The type of binary star being pursued by these researchers is a pre-extremely low mass (ELM) white dwarf, also referred to as an evolved cataclysmic variable. This is a transitional binary star that forms the connection between the Cataclysmic Variables and the Extremely-Low Mass White Dwarfs. It was theorized that the only way for an extremely low mass white dwarf to form is with the help of a binary companion. The idea being that the ELM white dwarf lost its outer envelope due to the gravitational pull from the companion star.

So far, astronomers observed both cataclysmic variables as well as ELM white dwarfs with normal white dwarf companions. However, it is the first time that also the transitional phase in between these two is observed: the moment the star has lost most of its mass and has nearly contracted to an ELM white dwarf.

 

Artist's depiction of a new type of binary star: a pre-extremely low mass (ELM) white dwarf. Pictured in blue, the star is losing mass to a white dwarf companion and transitioning to an ELM white dwarf. Credit: M. Weiss/Center for Astrophysics (Harvard & Smithsonian)

 

The combination of Gaia's Early Data Release 3 with data from the Zwicky Transient Facility (ZTF) forms the basis of this research paper. El-Badry et al. started with an initial query to the Gaia Archive, applied some quality cuts and extracted only the stars which show variability (as found from Gaia photometric uncertainty/variability diagnostics). Then, El-Badry et al. combined this sample with data from the ZTF and also on the ZTF side, cleaned up the sample using quality cuts and then did a further selection on variability parameters, hence narrowing down the sample to 50 potential candidates.

Kareem El-Badry emphazises the importance of public data from astronomical surveys for his work: "If it weren't for projects like the Zwicky Transient Facility and Gaia, which represent a huge amount of work behind the scenes from hundreds of people, this work just wouldn't be possible", he says.

Of the 50 candidates, 21 were followed-up by obtaining multi-epoch spectra using the Shane telescope of the Lick Observatory. The follow-up observations of these 21 candidates was highly successful: all 21 turned out to be pre-ELMs.

"100 percent of the candidates were these pre-ELMs we'd been looking for", says Kareem El-Badry. "They were more puffed up and bloated than ELMs. They also were egg-shaped because the gravitational pull of the other star distorts their spherical shape."

"We found the evolutionary link between two classes of binary stars - cataclysmic variables and ELM white dwarfs - and we found a decent number of them", El-Badry adds.

From the follow-up spectra, 13 of the stars showed signs that they were still losing mass to their companion. The other eight seemed no longer to be losing mass. El-Badry plans to continue studying the pre-ELM white dwarfs and may follow-up on the 29 other candidates he previously discovered.

 

Figure 2: HR diagram with the 21 pre-ELMs identified (indicated with the stars), some of which without emission lines (so likely detached) and some of which with emission lines (and likely still transferring mass). These are transitional between Cataclysmic Variable donors and ELM WDs. As a reference, a sample of Cataclysmic Variables is given (black crosses) and a sample of ELM WDs is given (pink crosses), both taken from literature. Credit: Kareem El-Badry, et al. 2021 MNRAS.

 

This is just one of the many amazing results coming out from Gaia's Early Data Release 3. The scientific community waits in anticipation for the first release of binary stars from Gaia in Gaia Data Release 3, which promises to bring a few 100,000 non-single stars and is a potential treasure chest for astronomers.

 

Further reading:

 

Credits: Kareem El-Badry, et al. 2021 MNRAS

 

Published: 01/12/2021

 

Image of the Week Archive

2021

01/12: Observation of a long-predicted new type of binary star

24/09: Astrometric microlensing effect in the Gaia16aye event

22/09: the power of the third dimension - the discovery of a gigantic cavity in space

16/09: An alternative Gaia sky chart

25/08: Gaia Photometric Science Alerts and Gravitational Wave Triggers

09/07: How Gaia unveils what stars are made of

23/06: Interviews with CU3

27/04: HIP 70674 Orbital solution resulting from Gaia DR3 processing

30/03: First transiting exoplanet by Gaia

26/03: Apophis' Yarkovsky acceleration improved through stellar occultation

26/02: Matching observations to sources for Gaia DR4

2020

22/12: QSO emission lines in low-resolution BP/RP spectra

03/12: Gaia Early Data Release 3

29/10: Gaia EDR3 passbands

15/10: Star clusters are only the tip of the iceberg

04/09: Discovery of a year long superoutburst in a white dwarf binary

12/08: First calibrated XP spectra

22/07: Gaia and the size of the Solar System

16/07: Testing CDM and geometry-driven Milky Way rotation Curve Models

30/06: Gaia's impact on Solar system science

14/05: Machine-learning techniques reveal hundreds of open clusters in Gaia data

20/03: The chemical trace of Galactic stellar populations as seen by Gaia

09/01: Discovery of a new star cluster: Price-Whelan1

08/01: Largest ever seen gaseous structure in our Galaxy

2019
20/12: The lost stars of the Hyades
06/12: Do we see a dark-matter like effect in globular clusters?
12/11: Hypervelocity star ejected from a supermassive black hole
17/09: Instrument Development Award
08/08: 30th anniversary of Hipparcos
17/07: Whitehead Eclipse Avoidance Manoeuvre
28/06: Following up on Gaia Solar System Objects
19/06: News from the Gaia Archive
29/05: Spectroscopic variability of emission lines stars with Gaia
24/05: Evidence of new magnetic transitions in late-type stars
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.