# Uncertainty of distance measurements for regions between 50-250 pc away

1. Dec 6, 2012

### Aiveenoka

Hi,

I am in the middle of a project dealing with the mass loss rate of protostars and hence I am working with the distance that these sources are away from us. I need to find the error in these distance measurements, however I cannot. In any paper (I find) that cites distances it just gives the number with no error values attached, and so I am wondering if there is a standard error in measuring the distance.

I am working with distances including 56pc (smallest), 140pc and 250pc (largest).

Thank you,
A

2. Dec 7, 2012

### Staff: Mentor

It depends on the object you measure and the telescope used for that.

The Hipparcos mission measured many stellar positions with an uncertainty of ~1milliarcsecond, this corresponds to the parallax of an object 2000pc away. If the parallax measurement has the same quality as the absolute position measurement (as relative measurement, I would expect a better accurary), this gives a relative uncertainty of ~1/80, ~1/14, ~1/8 for 56, 140, 250 pc respectively. GAIA is designed to improve parallax measurements to 10 microarcseconds*, reducing the relative error to <0.13% for the full range of your distances.

* similar to a coin (~2cm) on the moon

3. Dec 8, 2012

### Aiveenoka

Hi mfb,

The objects that have been measured are young stellar objects (YSOs) and unfortunately I don't know what was used to measure.
I had asked my supervisor about the error and he said it would be 5 or 10 pc or similar, however he is away now and so I cannot check anything with him. But I want to be able to back up my reasoning for taking the error to be whatever I use and I also didn't feel that I could "pick and choose" the errors, not to mention that the error for 56pc would be very different than for 250pc, hence I asked here.
When you say the error is about 1/80 for 56pc do you mean 56 +/- 0.0125pc ? If that is the case, that is amazing! Technology is fascinating!

Aiveenoka :)

4. Dec 8, 2012

### Staff: Mentor

It is possible to measure distances with that precision. It does not mean that every star has been measured with that precision.

A quick search lead me to this website: The hipparcos catalogue has the parallax (H11) together with its standard deviation (H16) as parameters.

5. Dec 11, 2012

### Aiveenoka

Thank you very much mfb :)

It's amazing what is possible!