Nucleo de Estudo e Observacao Astronomica - Jose Brazilicio de Souza (Florianopolis, Brazil) (NEOA-JBS)
Wed, 06/15/2022 - 12:39

Dear friends,

I'd like to share a curious observation.

In recent nights I'm noting that beta Hyi is brighter than alpha Hyi.

2022 June 12 at 08:43 TU
status: beta Hyi 0.2 brighter than alpha Hyi

2022 June 13 at 08:30 TU
status: beta Hyi 0.2 to 0.3 brighter than alpha Hyi

In both occasions it was predawn sky, with alpha Hyi at altitude ~45 deg and beta Hyi at ~39 deg, with setting moon at 13 june.

According to ICQ's Table Ib "Winter" atmospheric extinction for h = 0 km, the diference between correction values for zenithal distances 50 deg and 45 deg is:
0.38 - 0.35 = 0.03 magnitudes

But despite alpha Hyi was higher than beta Hyi, its visual magnitude was fainter in 0.2 and 0.3 magnitudes.

In my visual experience, I consider:

slightly brighter or fainter = a 0.1 magnitude difference

brighter or fainter = a 0.2 magnitudes difference

much brighter or much fainter = a >0.2 magnitudes difference

In GCVS, beta Hyi is catalogued as NSV 161 with range 2.75-2.81 V.

According to Bright Star Catalogue

alpha Hyi has mV = 2.86 (b-v = +0.28)
 beta Hyi has mV = 2.80 (b-v = +0.62)

So, at naked eye, alpha Hyi should be "slightly brighter than" beta Hyi or even equal.

After contact Sebastian Otero privately, we could have two situations at least:

#1: alpha Hyi is constant and beta Hyi's range is wide

#2: beta Hyi (NSV 161) has that little range, but alpha Hyi could be variable

In this 2nd scenario, assuming beta Hyi with mV = 2.8, the observed magnitude of alpha Hyi in those dates should be 3.0 and 3.1.

For visual monitoring, one way to elucidate this case is select another comps and pay attention to estimate both stars (alpha Hyi and beta Hyi) with comps near the same altitude to minimize effects of atmospheric extinction.

Otero quoted some comps:

alpha Mus (mV = 2.69, BSC)
 beta Mus (mV = 3.05)
gamma Gru (mV = 3.01)
alpha Cir (mV = 3.19)

I include to this list:

alpha Phe (mV = 2.39)
 beta TrA (mV = 2.85)
gamma TrA (mV = 2.89)

with regards,