Jing Li — Page 49 | Searcharxiv

arXiv2000

The Nature of Solar Polar Rays

We use time series observations from the SOHO and Yohkoh spacecraft to study solar polar rays. Contrary to our expectations, we find that the rays are associated with active regions on the sun and are not features of the polar coronal holes. They are extended, hot plasma structures formed in the active regions and projected onto the plane of the sky above the polar coronal holes. We present new observations and simple projection models that match long-lived polar ray structures seen in limb synoptic maps. Individual projection patterns last for at least 5 solar rotations.

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arXiv1996

The Milky Way, The Local Galaxies \& the IR Tully-Fisher Relation

Using the near infrared fluxes of local galaxies derived from COBE/DIRBE J(1.25 $μ$m) K (2.2 $μ$m) \& L (3.5 $μ$m) band maps and published Cepheid distances, we construct Tully-Fisher (TF) diagrams for the nearby galaxies. The measured dispersions in these luminosity-linewidth diagrams are remarkably small: $σ_J = 0.09$ magnitudes, $σ_K = 0.13$ magnitudes, and $σ_L = 0.20$ magnitudes. For the J and K bands, Monte Carlo simulations give a 95\% confidence interval upper limit on the true scatter in the T-F diagram of $σ_J \le 0.35$ and $σ_K \le 0.45$. We determine Milky Way's luminosity and place it in the T-F diagram by fitting a bar plus ``standard'' values of its size and circular speed (Sun-Galactic center distance $R_0 = 8.5 \kpc$ and $Θ_0 =220 \kms$), the Milky Way lies within $1.5 σ$ of the TF relations. We can use the TF relation and the Cepheid distances to nearby bright galaxies to constrain $R_0$ and $Θ_0$. Alternatively, we can fix the parameters of the Galaxy to their standard values, ignore the Cepheid zero-point, and use the Tully-Fisher relation to determine the Hubble Constant directly: $H_0 = 66 \pm 12$ km/s/Mpc.

astro-ph↗