Aktive Giant HD 12545 (XX Triangulum)

Stars are sometimes also very asymmetrical inside;
Pictures of the star HD 12545; (XX Triangulum) made by K. G. Strassmeier (University of Vienna) show the same phenomenon which we observe on the pictures of Uranus. It is a gas ball warmed from the inside by an asymmetrical heat source.

XX Triangulum

Strassmeier interprets this photograph as a “starspot” similar to the spots on the Sun.
Journal: Astronomy and Astrophysics, v.347, p.225-234 (1999)

The active K0 giant HD 12545 is the star with the largest starspots ever observed. We report a record light-curve amplitude of 0fm63 in V and 0fm17 in V-I in January 1998. At the same time, HD 12545 was at its brightest magnitude since the discovery of its light variability in 1985. We present the first Doppler image of HD 12545 from observations during this state of high-amplitude light variability and find that the star exhibits one cool high-latitude spot of gigantic dimensions
(~12×20 solar radii, i.e. 60 times the extension of the largest sunspot group or 10,000 times larger areal coverage). Furthermore, our map shows one smaller cool spot and one equatorial warm (bright) spot. The warm spot is situated approximately 180 degr from the large cool spot in the opposite hemisphere and is the cause of the exceptionally large light-curve amplitude and the stellar brightening.


The “starspot” analogous to the spots on the Sun, or something entirely different?

Comparing the “starspot” on XX Triangulum to the spots on the Sun raises serious doubts. On the one hand there is no coherent explanation in physics for the spots on the Sun themselves. The mechanism of the cycle of the spots on the Sun is one of the ‘Big Questions’ to which the physicists haven’t found an answer so far. So it is completely obscure on what basis does Strassmeier draw the analogy of the appearance of HD 12545 to something which rules he doesn’t know. On the other hand the shape itself and proportions of this spot in comparison to the radius of HD 12545 demand caution by such comparisons. The spots on the Sun usually occur in active regions of its surface. The active regions and spots on the Sun lead to explosions, protuberances and CMEs (Coronal Mass Ejections). If it was the same mechanism on the XX Triangulum, then the “starspot” should have exploded as a huge CME long time ago. With this size of the spot it must have been an explosion of the size similar to Nova and probably would cause the destruction of the star as a giant. But because the HD 12545 exists stably and does not explode then it is a proof for that what we see in the Doppler pictures of this star has nothing to do with the spots on the Sun. Strassmeier compares the unknown mechanism of origination of the spots on the Sun to another unknown mechanism of formation of the spots on HD 12545. Strassmeier seems to forget that HD 12545 and our Sun are two completely different types of stars:
– temperature on the surface of the Sun is about 2200°C higher than on HD 12545
– the difference between the radii of both stars is clearly visible on the picture
– the Sun still belongs to the main series on the HR Diagram while the HD star does not.
That is why the introduction of analogy of HD 12545 to the Sun doesn’t explain anything but only increases the already big confusion in astrophysics. The situation also won’t be improved by purely numeral comparisons showing that the size of the spot on HD 12545 is tens times bigger than the spots on the Sun or that its surface is 10,000 times bigger. Qualitatively these information don’t bring anything new to the problem. They only underline the helplessness of astrophysics in both cases: mechanism of formation of the spots on the Sun and on the HD 12545.
The only simple and logical explanation of such temperature distribution on the surface of HD 12545 that we see in Doppler images is a big asymmetry of the hot interior of this star, just as in case of Uranus.
The internal asymmetry of this star is enlarged by the fact that it is a component of a double system in which two stars revolve round their common center of gravity. That is why the orbital centrifugal force is bigger than in the case of revolution only round the center of galaxy.

[T. Tumalski; April, 2001)]

Tadeusz Tumalski
ul. Wrzosowa 8
09- 401 Plock

Mob. +48 698 432 899


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