HD 209458 (F8-G0V színképtípus)

Égi koordináták (2000): RA= 22 03 10.7, Dec= +18 53 04 (Pegazus)

 fényessége: V=7.65 mag,    távolsága: d=153 fényév

magyar nyelvű ismertető az [origo]-ban

IAU Cirkulárok hírei:
No. 7307, 1999 November 12  Daniel W. E. Green
Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION
URL http://cfa-www.harvard.edu/iau/cbat.html
HD 209458
G. W. Henry, Tennessee State University; G. Marcy, University of California at Berkeley; R. P. Butler, Department of Terrestrial Magnetism, Carnegie Institution of Washington; and S. S. Vogt, Lick Observatory, report: "The G0 V star HD 209458 = BD +18 4917 (R.A. = 22h03m10s.78, Decl. = +18o53'03".5, equinox 2000.0; V = 7.65) exhibits sinusoidal velocity variations with a semiamplitude of 81 m/s, indicating the presence of a companion with M sin i = 0.63 Jupiter mass and an orbital period of 3.523 days. Photometry reveals a transit ingress on Nov. 8.20 UT with a depth of 0.017 mag,
consistent with the transit time predicted from the velocities. Further measurements of transits and velocities would be valuable.
The next three predicted times of ingress occur at Nov. 15.263, 18.787, and 22.311 (all times uncertain by 1 hr). If correct, the inferred mass is 0.63 that of Jupiter, and radius 1.6 that of Jupiter, implying a density of 0.21 g/cm^3. HD 209458 resides at a distance of 47 pc, with rotational v sin i = 3 km/s, and is chromospherically inactive, with an estimated age of 4.5 Gyr."

Circular No. 7314, 1999 November 22
R. Rebolo, M. R. Zapatero Osorio, H. J. Deeg, and J. Licandro, Instituto de Astrofisica de Canarias; and J. Marti, University of Jaen, report: "CCD photometry of the star HD 209458 obtained at the 1.5-m Spanish Telescope at Calar Alto reveals a transit egress of the planet reported on IAUC 7307, with a depth of 0.023 +/- 0.005 mag, on Nov. 18.87 UT. Ingress started before observations, but assuming an orbital period of 3.523 days, the transit lasts 3.0 +/- 0.1 hr. Best fits give an orbital inclination of 87.0 +/- 0.5 deg and a planet radius 1.34 +/- 0.07 that of Jupiter." R. A. Street, T. A. Lister, A. Cameron, and K. Horne, St. Andrews University, report that 640-nm narrowband CCD photometry of HD 209458 with the 0.9-m Gregory telescope in St. Andrews confirms that a planetary transit with depth of 0.019 +/- 0.003 mag occurred from Nov. 18.760 +/- 0.021 to 18.903 +/- 0.031 UT. Z. Ioannou, C. Hellier, R. D. Jeffries, and T. Naylor, Keele University, report that V-band photometry with the 0.6-m telescope at Keele Observatory are consistent with an egress as reported above, but the increasing airmass makes the data from this time onwards unreliable. For further details, see http://star-www.st-and.ac.uk/~ras11/indexPS.html."

Circular No. 7315, 1999 November 22
In response to a request from the Central Bureau, D. W. Latham, Harvard-Smithsonian Center for Astrophysics, communicates on behalf also of D. Charbonneau, T. M. Brown, M. Mayor, and T. Mazeh: "We have prepared an updated ephemeris for the transits of HD 209458. This ephemeris is based on 150 velocity observations dating back to Aug. 1997 (made with HIRES on Keck I, as part of the G Dwarf Planet Search under NASA time, with ELODIE on the 1.93-m
telescope at Observatoire de Haute Provence, and with CORALIE on the new Swiss 1.2-m telescope at La Silla; a paper describing the spectroscopic results is in preparation) and on two complete transit observations obtained on 1999 Sept. 8 and 15 (made by Charbonneau and Brown with the STARE instrument at the High Altitude Observatory, National Center for Atmospheric Research, Boulder, and reported in a paper submitted to Ap.J. Lett. by Charbonneau, Brown, Latham, and Mayor). G. Torres has carried out a simultaneous solution of the radial velocities and the transit observations and provided the following orbital period and epoch of transit center: P = 3.52433 +/- 0.00027 days, T_c = 2451430.8238 +/- 0.0033 (HJD). Predictions for the center of the transits through the end of Dec. 1999 are: HJD 2451508.3590 +/- 0.0080,
2451511.8833 +/- 0.0083, 2451515.4077 +/- 0.0086, 2451518.9320 +/- 0.0089, 2451522.4563 +/- 0.0091, 2451525.9806 +/- 0.0094, 2451529.5050 +/- 0.0097, 2451533.0293 +/- 0.010, 2451536.554 +/- 0.010, 2451540.078 +/- 0.011, 2451543.602 +/- 0.011. Observers should plan to monitor the star for at least 2 hr before and after these times of transit center. Our identification of HD 209458 as a prime target for transit observations was made possible by the
many contributions of the G Dwarf Planet Search, ELODIE, and CORALIE teams: J. L. Beuzit, M. Burnet, G. A. Drukier, D. Naef, F. Pepe, C. Perrier, D. Queloz, N. Santos, J. P. Sivan, G. Torres, S. Udry, and S. Zucker."

Circular No. 7317, 1999 November 24
G. Gonzalez, University of Washington, writes that he obtained differential CCD photometry of HD 209458 during Nov. 22.07-22.35 UT, using the the Manastash Ridge Observatory 0.76-m telescope, with C. Laws and M. Braunstein. An 8-nm-side filter centered at 673 nm was used to obtain images every about 3 min. They detect a dimming of HD 209458 starting at Nov. 22.28 +/- 0.015 day, but they did not observe long enough to see last contact, due to the low altitude of the star. They estimate that the dimming amounted to about 0.028 mag (using two comparison stars that were each about 4
mag fainter than HD 209458).

Circular No. 7323, 1999 December 1
E. Poretti, Brera Astronomical Observatory, writes: "Forty-six V photoelectric measurements of HD 209458 obtained with the Merate 0.5-m telescope show that a transit (depth 0.016 +/- 0.002 mag) started at Nov. 25.815 UT. Observations began at Nov. 25.74, but stopped at Nov. 25.91 due to large airmass, before egress. Analysis of B photometry is in progress."
Independent reports have been received from S. Soderhjelm, Lund Observatory; and from N. Robichon and F. Arenou, DASGAL, Observatoire de Paris, Meudon, of the existence of five HD 209458 transits in 89 separate Hipparcos photometric measurements obtained between 1991 Apr. 17 and Nov. 4. Robichon and Arenou report that the mean depth of the transits is 0.025 +/- 0.004 magnitude in the Hipparcos H_p band, corresponding to a relative depth in the flux of 2.3 +/- 0.4 percent (results submitted to A.Ap.). Using the epoch T_c of Charbonneau et al. (submitted to Ap.J. Lett.; see also IAUC 7315),
periods of 3.524738 +/- 0.000015 (Robichon and Arenou) and 3.52473 +/- 0.00005 (Soderhjelm) days have been derived. Soderhjelm's details will appear on IBVS 4816.

                                                 A mért radiális sebesség (pontok) és az illesztett görbe.

                                    Az előző ábra adatai egy keringésre összenyomva (fázis-diagram).

A HD209458b bolygó pályaadatai:

Paraméter számolt érték
Keringési periódus 3.528 nap 
Radiális sebesség félamplitudó (K) 81 +/- 3 m/s 
Pálya félnagytengely 0.045 Cs.E. 
Excentricitás 0.01 +/- 0.03 
M sin i (M Jup) 0.63 

A Nap és a HD209458 összehasonlítása:
Paraméter Nap HD209458 Forrás
T (Kelvin) 5780 6000 .
Mv 4.79 4.29 Hipparcos. 
Log grav (cgs) 4.45 4.31 Blackwell et al, 1994, A&A, 282, 899 
Színképtípus G2V F8V SIMBAD 
R'hk -4.937 -4.93 Keck/HIRES H&K Line 
P rot (nap) 25.4 ~30 +- 10 d from chromospheric K-line (Noyes et al.)
Vsin i (km/s) 1.8 3 Keck/HIRES Spectrum 
[Fe/H] 0.00 Unknown?
Kora = 3-7 Gyr, from H&K line, and Noyes et al. (1984)

            A csillag fényességének változása a bolygó előtte való átvonulása miatt.

                   November 18.: A csillag fényességének változása a bolygó előtte való átvonulása miatt.