Image of the Week

Short period/faint magnitude Cepheids in the Large Magellanic Cloud observed by Gaia

   
  G-band light curves of short period/faint Cepheids in the Large Magellanic Cloud observed by Gaia during 28 days of EPSL and 3 days of NSL, processed through the full chain of the CU7 pipeline. The light curves were folded according to the periods derived by the CU7 Cepheid&RR Lyrae SOS pipeline. A few (1-3) observations with estimated uncertainties larger than 0.05 mag were excluded from the plots. Median uncertainties of the measurements are around 10-15 mmag. All light curves cover 2 pulsation cycles.  
 

In December 2014 a first reduction of the photometry acquired by Gaia during 28 days of Ecliptic Pole Scanning Law (EPSL) and 3 days of Nominal Scanning Law (NSL) was delivered to CU7, the Coordination Unit in charge of performing the analysis of the variable sources observed by Gaia. In the week of 19-25 March 2015, the full chain of the CU7 pipeline ran on the EPSL+NSL dataset (about 800,000 sources which have more than 20 Field-of-View transits), starting from the general Variability Detection, general Characterization, proceeding through the global Classification and ending with the detailed checks and typecasting of the Specific Objects Study (SOS). The time-series photometry of 1242 sources in the South Ecliptic Pole (SEP), which covers an external region of the Large Magellanic Cloud (LMC), was fed into the Cepheid&RR Lyrae SOS pipeline, which returned a rich harvest of LMC RR Lyrae stars (more than 800, including some hundreds of new discoveries, with typical average magnitudes around G~19.5 mag and periods in the range of about 0.15  to 1.0 days) and a few Cepheids at the short period/faint end of the LMC Cepheids period-luminosity distribution. Some of them are new Cepheids discovered by Gaia.

The figure above shows the G-band light curves of five of these Cepheids folded according to the periods determined by the CU7 Cepheid&RR Lyrae SOS pipeline. They have average G magnitudes in the range of 18.3 to 18.7 mag and periods ranging from 0.3 to 1.93 days, hence partially overlapping with the RR Lyrae stars.

The light curves consist (from top to bottom) of  56, 44, 39, 49 and 31 observations, each corresponding to 9 individual CCD observations, spread over a total time span of 32 days. A few (1-3) observations with estimated uncertainties larger than 0.05 mag were excluded from the plots. Median uncertainties of the measurements are around 10-15 mmag.

The sample in the figure includes one first-overtone classical Cepheid (upper panel), 3 candidate anomalous Cepheids (central three panels) and a candidate Type2 Cepheid (bottom panel). The classification in sub-types provided by the Cepheid&RR Lyrae SOS pipeline will be refined as improved BP and RP time-series become available for these sources.

The Cepheids in the four upper panels were classified as Cepheids either in the OGLE III (Soszynski et al., 2008, Acta Astron., 58, 163) or in the EROS-2 (Kim et al. 2014, A&A, 566, A43) catalogues of LMC variable stars. OGLE III specifically confirms our classification as first-overtone classical Cepheid for the source in the upper panel of the figure. Conversely, the Cepheid in the lower panel has a counterpart in the EROS-2 catalogue which Kim et al. (2014) classify as an eclipsing binary, while Gaia data show the star as a Cepheid with no obvious sign of binary component.

Photometry for brighter Cepheids known in the LMC (whose magnitude distribution peaks at G~15.5 mag) was not produced with this first data reduction, but will soon become available with the reprocessing of the full EPSL data stream.

The nominal scanning law yieds a different cadence than achieved with EPSL data. Nevertheless, the examples above can be used to assess the scientific performance. On average Gaia observes every source 70 times during the nominal 5 year operational period, providing a roughly similar phase coverage for short period variables.

These five faint Cepheids demonstrate the great potential of Gaia's photometry and the excellent performance of the CU7 pipeline.


Credits: ESA/Gaia/DPAC/CU5/DPCI/CU7/INAF-OABo/INAF-OACn Gisella Clementini, Vincenzo Ripepi, Silvio Leccia, Laurent Eyer, Lorenzo Rimoldini, Isabelle Lecoeur-Taibi, Nami Mowlavi, Dafydd Evans, Geneva CU7/DPCG and the whole CU7 team. The photometric data reduction was done with the PhotPipe pipeline at DPCI; processing data were received from the IDT pipeline at DPCE.

[Published: 28/05/2015]

 

Image of the Week Archive

2017
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
 
Please note: Entries from the period 2003-2010 are available in this PDF document.