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The roles of rotation and pulsation in the new B- and A-type periodic variables in NGC3766 Nami Mowlavi, + S. Saesen, T. Semaan, P. Eggenberger,F. Barblan, L. Eyer, S. Ekstrm, C. Georgy (University of Geneva, Switzerland) * New variable

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 1

Nami Mowlavi, + S. Saesen, T. Semaan, P. Eggenberger,F. Barblan, L. Eyer, S. Ekström, C. Georgy (University of Geneva, Switzerland)

The roles of rotation and pulsation in the new B- and A-type periodic variables in NGC3766

* New variable stars in NGC 3766 : Reminder → Mowlavi et al. (2013, Paper I) * VLT spectra : New insight → Mowlavi et al. (2016, submitted)

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 2

Christensen-Dalsgaard (2004)

log Teff log L/L⊙

6 4 2 4.0 3.5 4.5 5.0

SPB stars

0.5 - 5 d

δ Sct stars 0.02-0.25 d γ Dor stars 0.3-1.7 d β Cep stars 0.1-0.6 d Stellar pulsation in the HR diagram

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 3

log Teff log L/L⊙

6 4 2 4.0 3.5 4.5 5.0

X

No pulsation Stellar pulsation in the HR diagram

Christensen-Dalsgaard (2004)

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 4

Open cluster NGC 3766

14 - 30 My

→ 2545 images in V’ 430 images in B’ 376 images in U’

1’

ESO Press Release 1326 (2013)

  • Photom. survey 2002-2009

(1.2m Euler telescope, La Silla)

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 5

Mowlavi et al. (2013)

  • Photom. survey 2002-2009

(1.2m Euler telescope, La Silla)

Open cluster NGC 3766

14 - 30 My

107

SPB δ Sct γ Dor new periodic variables

Mowlavi et al. (2013)

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 6

* Maia stars (?) Struve (1955), ... , Scholz et al. (1998) * Individual stars Ex: Waelkens et al (1998), Aerts & Kolenberg (2005) * CoRoT

Yes, pulsation proposed (Degroote et al. 2009)

* Kepler

Yes, spots proposed (Balona 2013) * NGC 7654 Yes, but not recognized as such (Luo et al 2012)

Previously reported periodic variables in the gap ? Before Paper I (not exhaustive) Since 2013 (not exhaustive)

  • Lata et al. (2014) “Main-sequence variable stars in young open cluster NGC 1893”
  • Lata et al. (2016) “Variable stars in young open star cluster NGC 7380”
  • Balona et al. (2016) “The hot γ Doradus and Maia stars"
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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 7

Properties of the new group

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Period (day) 0.0 2.5 5.0 7.5 10.0 Number of stars

NGC 3766

Period 0.1 – ~0.5 d

1 2 3 4 5 6 7 8 9 10 11 Amplitudes (mmag) 0.0 2.5 5.0 7.5 10.0 12.5 Number of group 2 stars

NGC 3766

Limited by photometric precision → extends below mmag

Amplitude <1 – ~5 mmag

Mowlavi et al. (2013)

Shorter than SPBs and longer than δ Scts

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 8

Origin of variability? Binary stars ? Role of rotation ? ← multi-epoch Vr ← v*sin(i)

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 9

Origin of variability? Spectra taken with VLT/Girafe (LR02 mode) for

  • all new variables
  • SPB stars
  • Many non-periodic stars in same mag range

Multi-epoch: for each star, several spectra each night during three consecutive nights ← multi-epoch Vr ← v*sin(i) Binary stars ? Role of rotation ?

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766

2 4 6 8 10 12

NGC 3766 New variability class

Binaries P 1>0.55 d P 1<0.55 d

100 200 300 400 v sini (km/s) 1 2 3 4 5

SPB

Hybrid

Number of stars

10

Rotation rates

Mowlavi et al. (2016)

Result 1: New variables form 2 groups

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766

2 4 6 8 10 12

NGC 3766 New variability class

Binaries P 1>0.55 d P 1<0.55 d

100 200 300 400 v sini (km/s) 1 2 3 4 5

SPB

Hybrid

Number of stars

11

Rotation rates

Mowlavi et al. (2016)

Result 1: New variables form 2 groups

Group 1 P1 > 0.55 d small v*sin(i) Group 2 P1 < 0.55 d Fast-rotators

} }

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 12

Rotation rates Result 1: New variables form 2 groups

  • SPB

FaRPB δ Scuti γ Dor

51 58 70 84 107 154 278 298 364

NGC 3766

10 11 12 13 14 15 V' (mag) 0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00 P phot (d)

50 100 150 200 250 300 350

v sini (km/s)

Mowlavi et al. (2016)

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 13

Rotation rates Result 1: New variables form 2 groups

  • SPB

FaRPB δ Scuti γ Dor

51 58 70 84 107 154 278 298 364

NGC 3766

10 11 12 13 14 15 V' (mag) 0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00 P phot (d)

50 100 150 200 250 300 350

v sini (km/s)

small v*sin(i) FaRPB

Fast Rotating Periodic B-type

}

Mowlavi et al. (2016)

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766

SPBs β Ceps

14

de Cat (2002)

Expected amplitude of RV variations β Ceps: AVr <~20 km/s SPBs: AVr <~ 7 km/s

Vr → Binarity ?

→ Binary if AVr >~ 20km/s

Identification of binaries

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766

  • 36

51 68 84 107 154 175 278 364

1 2 5 10 A 1 (mmag) 10 20 30 40 50 60 Q RV (km/s)

50 100 150 200 250 300 350

v sini (km/s)

NGC 3766

Binaries

15

Binary stars Identification of binaries

Mowlavi et al. (2016)

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 16

Binary stars

  • ●
  • ●
  • ●
  • ●
  • ●
  • ●
  • −30

−20 −10 RV (km/s)

NGC3766−154: Pphot = 0.80672 d [ Porb >> 3 d ]

  • ●

−40 −20 20 40 RV (km/s)

NGC3766−278: Pphot,1 = 0.62115 d, Pphot,2 = 0.199088 d [ Porb = 2*Pphot,1 ]

  • 0.0

0.5 1.0 1.5 2.0 MJD − 56765 d −100 −50 50 100 RV (km/s)

NGC3766−364: Pphot = 0.91772 d [ Porb = 2*Pphot ]

  • ●
  • ●
  • ●
  • ●
  • ●
  • ●
  • ●
  • ●
  • ●
  • ●
  • 0.0

0.5 1.0 1.5 2.0 MJD − 56765 d −150 −100 −50 50 100 RV (km/s)

NGC3766−107: Pphot = 4.536 d [ Porb = Pphot ]

0.0 0.5 1.0 1.5 2.0 MJD − 56765 d −150 −100 −50 50 100 RV (km/s)

Identification of binaries

Mowlavi et al. (2016)

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 17

Rotation rates Result 1: New variables form 2 groups

  • SPB

FaRPB δ Scuti γ Dor

51 58 70 84 107 154 278 298 364

NGC 3766

10 11 12 13 14 15 V' (mag) 0.02 0.05 0.10 0.20 0.50 1.00 2.00 5.00 P phot (d)

50 100 150 200 250 300 350

v sini (km/s)

Mowlavi et al. (2016)

FaRPB

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 18

  • ●
  • ●
  • ●
  • ●
  • FaRPB stars with v sini ≥ 250 km/s

NGC 3766

11.0 11.5 12.0 12.5 13.0 13.5 V' (mag) 0.1 0.2 0.3 0.4 0.5 P phot (d)

260 280 300 320 340

v sini (km/s)

P-L relation Result 2: New Period-Luminosity relation

(solid line)

Mowlavi et al. (2016)

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 19

P-L relation Cepheid-like pulsation mechanism ?

  • ●
  • ●
  • ●
  • ●
  • FaRPB stars with v sini ≥ 250 km/s

NGC 3766

11.0 11.5 12.0 12.5 13.0 13.5 V' (mag) 0.1 0.2 0.3 0.4 0.5 P phot (d)

260 280 300 320 340

v sini (km/s)

Result 2: New Period-Luminosity relation

→ (dotted line) Marginal agreement

Mowlavi et al. (2016)

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 20

P-L relation + factor of 2 between the two sequences Result 2: New Period-Luminosity relation Rotation-related ?

→ (dashed line)

  • ●
  • ●
  • ●
  • ●
  • FaRPB stars with v sini ≥ 250 km/s

NGC 3766

11.0 11.5 12.0 12.5 13.0 13.5 V' (mag) 0.1 0.2 0.3 0.4 0.5 P phot (d)

260 280 300 320 340

v sini (km/s)

Better agreement

Mowlavi et al. (2016)

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 21

Geneva isochrones

  • ●
  • ●
  • ●
  • 58

278 298

NGC 3766

FaRPB stars

11.0 11.5 12.0 12.5 13.0 13.5 V' (mag) 0.1 0.2 0.5 P phot (d)

50 100 150 200 250 300 350

v sini (km/s)

P-L relation Result 2: New Period-Luminosity relation

log(age[y]) : 7.4 7.2

Rotation rates from model predictions

d = 2.3 kp

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 22

Fast-rotating stars: ωcorot << Ω for prograde sectoral modes (m= −ℓ)

(e.g. Townsend 2005, Salmon et al. 2014)

Result 2: New Period-Luminosity relation P-L relation Origin: Pulsation in fast rotating stars?

ωobs ≃ ωcorot − mΩ (m: azimuthal order)

→ ωobs ≃ −mΩ

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  • N. Mowlavi 15/09/2016 STARS 2016

The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 23

P-L relation Result 2: New Period-Luminosity relation

  • ●
  • ●
  • ●
  • ●
  • FaRPB stars with v sini ≥ 250 km/s

NGC 3766

11.0 11.5 12.0 12.5 13.0 13.5 V' (mag) 0.1 0.2 0.3 0.4 0.5 P phot (d)

260 280 300 320 340

v sini (km/s)

m = −1 m = −2 prograde sectoral modes

FaRPB stars = Fast Rotating Periodic B-type stars Pulsating

Origin: Pulsation in fast rotating stars?

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The roles of rotation and pulsation in the new B- and A-type periodic variable stars in NGC3766 24

Conclusions

  • All new variables with P < 0.5 d are fast rotators

→ FaRPB stars (Fast Rotating Pulsating B-type) stars

  • They obey a new P-L relation

→ 2 sequences (maybe 3) Most probably prograde sectoral modes at ℓ = 1 and 2 Details in Mowlavi et al. (2016, submitted)